CHAPTER VIII.

THE MINE COMMAND.

A mine command consists of the mine groups and rapid-fire batteries specifically assigned for their protection, which are controlled by a single individual.

The mine commander is in direct command of the elements of the mine defense during drill and action. His station is at the mine primary, which is connected by telephone to the battle commander’s station. He bears the same relation to the battle commander as do the fire commanders, and his duties are similar to theirs.

The mine commander is responsible that the property officer requests for all matériel necessary to carry out the approved scheme for mining the harbor; he is responsible, further, that the property officer keeps this matériel in proper condition for immediate service.

The senior company officer of the mine command is the property officer and obtains from the district artillery engineer all necessary matériel for the mine defense. He has direct charge of the storeroom, cable tanks, loading room, wharves, boats, boathouses, and mining casemate. The personnel of the mine companies are subject to his orders for service in connection with caring for and maintaining this matériel.

The officers of the companies of the mine command will be assigned by the mine commander in accordance with their special fitness.

The enlisted personnel of mine companies will be divided into sections, detachments, and details, as follows:

(_a_) Fire-control and power section. (_b_) Planting and loading section. (_c_) Gun and ammunition sections. (_d_) Reserve section.

These will be subdivided as follows:

(_a_) Fire-control and power section: 1. Observing detachment— _a._ M′ detail. _b._ M″ detail. _c._ M‴ detail. 2. Plotting detachment— _a._ Plotting board detail. _b._ Communication detail. 3. Power detachment— _a._ Casemate detail. _b._ Searchlight detail. (_b_) Planting and loading section: 1. Planting detachment— _a._ Planter detail. _b._ Small-boat details. 2. Loading detachment— _a._ Loading room detail. _b._ Explosive detail. _c._ Cable detail. (_c_) Gun and ammunition section: _a._ Gun details. _b._ Projectile detail. _c._ Powder detail. (_d_) Reserve section: As required.

In each company assigned to the mine defense, a permanent manning table will be made out and always kept up to date. A copy of this manning table will be posted in the mine commander’s station. In addition, a copy of such portion of this table as pertains to any particular station will be posted therein.

=Plotting board.=—The plotting board differs from that used for guns in that it requires no gun arm and corresponding attachments. Furthermore, since the distance at which mines are planted will in general be small, the board, without any change in size, may be used with a much larger scale, say, 150 yards or even 100 yards to the inch, and the arms graduated accordingly.

The stations are manned during the planting of mines and the location of distribution boxes, as well as during operations.

[Illustration: FIG. 15.—PREDICTION RULER.]

For planting buoys signals may be made from the primary, from the secondary, or from both, as conditions warrant.

Observations are taken on each mine as planted, the data are recorded, and the position of each mine is plotted.

During operations vessels may be tracked by the vertical or by the horizontal method of position finding. If by the former, either the command “Fire” may be given when the vessel is on the cross wires of the instrument set at the range and azimuth of a mine, or the time from any point to the instant of passing over a mine may be found by means of the prediction ruler (see below) and the command “Fire” be given at the proper instant, as indicated by the stop watch. For the horizontal base system the latter method must be used.

=Prediction ruler= (fig. 15).—This is a 10-inch white celluloid slide rule with a beveled edge. The slide is graduated in “Yards in 15 seconds,” and on the left and right of the runway, respectively, are a “Fire at time” and a “Yards to mine” scales. The beveled edge is graduated from the center outward in both directions with “0” in the center of the scale and “500” at either end. Each 50 and 100 has its value engraved on the scale.

_Method of using._—Plot the position of the target for a 15-second interval. With the beveled edge find the distance the target has passed over during the interval; and also determine the distance from the last plotted position to the mine. Move the slide until the graduation corresponding to the “Yards in 15 seconds” is opposite the graduation corresponding to the “Yards to mine,” and read the “Fire at time” scale opposite the arrow on the slide. The reading will be the number of seconds from the last plotted position to the mine which the vessel is approaching. A stop watch is started at the time of the last observation on the target, and at the expiration of the time obtained from the “Fire at time” scale the command “Fire” may be given.

=Observation firing.=—The mine commander’s station is connected with the casemate by telephone. At the command “Observation firing” sent to the casemate, the casemate operator will see _that all automatic switches are up, and that all firing switches are open_. He will then close the double circuit breaker, and switches 4 and 9, which will energize the busses of the power panel. At the command “Group ——, mine ——,” the operator will close switches 3 and 8 on the power panel, thereby putting both D. C. and A. C. power on the operating boards. At the command “Ready,” given from the mine commander’s station at the proper time, the operator will stand ready to trip the corresponding automatic switch. At the command “Fire” the automatic switch will be tripped and the firing switch will be closed. Without delay, after the mine is fired, the firing switch and the power switch will be opened, the automatic switch closed up, and the mine switch opened on the mine block.

If the mine is struck before the command “Fire” is given, the automatic switch will fall, and the mine should be fired by closing the firing switch unless there are positive orders to the contrary.

=Contact firing.=—For contact firing the mine system will be set so that a signal will be sent to the casemate and the mine will be fired when the latter is struck by a passing vessel. This is the normal method of firing in actual service. At the command “Contact firing,” which may be given for all groups, or certain individual ones, the casemate operator will see _that all automatic switches are up, power and mine switches closed, and firing switches open_; he will then close the double circuit breaker, and switches 4, 9, 3, and 8 on the power panel. This puts both D. C. and A. C. on the operating boards. He will then close the firing switches on all the boards or on such as may have been indicated. When a mine has been fired, the corresponding mine block will be cut out.

If it is desired to delay the firing of a mine after being struck, the command “Delayed contact firing” is given. The operations are the same as for contact firing except that the firing switch is closed by the operator a short time after the mine has been struck or when directed to do so. After the mine has been fired the firing switch will be opened, and the corresponding mine block will be cut out.

APPENDIX NO. 1.

EXPLOSIVES.

The latest adopted explosive for submarine mines is trinitrotoluol, also called trotol. The commercial names for this explosive are trinol, trotyl, and triton.

Wet guncotton is used extensively for submarine mines and in emergency other commercial high explosives may be employed, preferably dynamite.

=Trotol= is a fine crystalline yellow powder, much resembling brown sugar. It is manufactured by nitrating toluol. It is very insensitive to shock or friction, insoluble in water, very stable in storage, and very powerful when detonated. Its melting point is about 81° C., its ignition point is about 197° C., its specific gravity in powdered form is about 1.55; it has no dangerous chemical action on metals.

The priming charge is a fuse can full of crystalline trotol.

Trotol is supplied in wooden boxes doubly lined with wax paper, each box containing about 50 pounds of explosive. The date of receipt at the post and the name of the explosive shall be painted on each box. The boxes should be stored in tiers with the marked end out, the bottom tier resting on skids. The explosive is not dangerous to handle, but the same care should be observed in storing and handling as with other high explosives. It should be stored in a perfectly dry place, preferably in a magazine. If it is impracticable to store in a magazine, the explosive may be stored in the driest place available where it is protected thoroughly from all fire risks. If from any cause the boxes of explosive are wet and there is reasonable assurance that the interior has become wet, a box should be selected and opened. If the interior is wet, a full report of the circumstances shall be made to the War Department. Boxes should be opened and the contents dried in open air out of the direct rays of the sun.

Trotol may be stored with wet guncotton, explosive D, and dynamite.

Inspection at posts will be limited to seeing that the rules for storage and care are strictly observed. Technical inspections will be made, when required, by the Ordnance Department.

=Wet guncotton= in the form of compressed cakes is supplied in boxes lined with zinc, the lid being screwed down upon a rubber gasket so as to prevent the loss of water by evaporation. Each box contains 100 pounds of dry guncotton. In the lid is a small flush cap which screws down upon a rubber washer and closes a tube communicating with the interior of the box. Upon each box there is painted by the manufacturer the net and total weights. Shipping regulations require that guncotton should be wet with water so that the water is 20 per cent of the weight of guncotton and water. This is too much water for full detonation, and the guncotton upon receipt at a post should be dried out so that the weight of water is from 12 to 15 per cent of that of the dry guncotton. The guncotton is dried by opening the box and pyramiding the guncotton on the lid and in the box so that there will be free circulation of air between the cakes. The use of an electric fan in this connection will ordinarily materially facilitate the operation. By weighing pilot cakes it may be determined when the proper amount of water has evaporated. The guncotton is then repacked, lid screwed down, and the weight chalked upon the end of the box. The guncotton should be placed while drying so that it is not in the sunlight and should be handled with clean cotton or rubber gloves.

In addition to the regular monthly inspection the boxes are reweighed quarterly under the supervision of the officer responsible for submarine mine explosive, and the gross weight so found chalked upon the end. Should any box show any decided decrease in weight the screw cap in the lid is removed, enough fresh water, preferably distilled or rain water, added to bring it up to its original weight, and the screw cap replaced.

Magazines in which guncotton is stored should not be allowed to attain a temperature as high as 100° F. for any length of time.

Guncotton which is kept wet may deteriorate after long storage, but will not become dangerous.

Wet guncotton can not be ignited by a flame, but gradually smoulders away as the outer portions in contact with the flame become dried.

A brownish or reddish shade is sometimes seen in cakes of guncotton. This is due to the presence of iron in the wash water and does not indicate decomposition.

When storing guncotton in the magazine the piles of boxes should be made so as to give free circulation of air and the greatest convenience in handling consistent with the capacity of the magazine.

In the event of damage to any case, which may cause loss of water by evaporation, the contents shall be removed at once, repacked in a guncotton box which has been washed with soda solution, the proper amount of water added to the contents, and the box closed. The gross weight shall be marked on the case. In repacking avoid as much as possible handling the cakes with the bare hands. This is for the protection of the guncotton from oil or acid of any kind. Clean cotton or rubber gloves are suitable covering for the hands when engaged on this work.

If for any reason the cases are subjected to dampness sufficient to cause unusual deterioration of the cases, they should be removed from the magazine and dried, out of the direct rays of the sun.

Guncotton containing 12 or 15 per cent of moisture may be stored with explosive D, trotol, and dynamite, but never with dry guncotton.

Empty cases, before being placed in storage, must be washed thoroughly to remove all traces of guncotton.

For a charge of wet guncotton, the priming charge is dry guncotton. This may be either of crumbled guncotton or cakes made to fit the fuse can. The compressed primer cakes are supplied wet and bored with holes to receive the fuses and the loading wire.

Should the supply of guncotton primers become exhausted fresh ones may be prepared as follows: Two blocks of soft pine are used, one 3 inches square, the other circular and 2.9 inches in diameter. A cake of wet guncotton is clamped between these blocks. Using a fine joiners’ saw and the circular block as a gauge, a cylinder is sawed from the cake. The cylinder is then smoothed down with a rasp. Four of these are prepared for each charge and in each one of them a hole about ⁹/₁₆ inch in diameter is bored. While boring the hole the cake must be tightly clamped between two pine blocks to prevent it from splitting; to insure that all the holes will be in alignment it is advisable that the upper wooden block be provided with a ⁹/₁₆-inch hole and be thick enough to enable this hole to serve as a guide for the bit. The boring is done with the ordinary bit, which must be sharp, so as to cut clean. _It is not safe to saw or bore a dry guncotton cake._

It is essential that the guncotton primer be thoroughly dry. The primers may be dried by exposure to the air or by means of drying ovens supplied especially for the purpose. To air-dry a primer, it is placed on edge upon a shelf of wire gauze or netting which is hung up indoors where there is a free circulation of dry warm air. Drying should continue until weighings on two successive days show no appreciable loss. This may require a week or more.

In drying with an oven the cakes are laid on edge on the shelves and the temperature of the oven is kept at about 100° F.; it should not exceed 104° F. The heat is provided by means of a bank of lamps placed under the hood and the current of warm air regulated by the size of the lamp bank and the openings in the top of the oven. Under no circumstances must an open flame be used as a source of heat. The drying in this case also is continued until successive weighings of samples show no appreciable loss.

Whenever it is necessary to dry more than 50 pounds of guncotton primers for immediate use the guncotton should be placed in the drying oven and exposed to the action of an electric fan placed about 4 feet in front of the open door until the moisture content is reduced to about 6 per cent, when the drying should be completed by the use of the bank of lamps as described in the preceding paragraph.

In each case, to test the dryness of the primers, take a cake and split it in four or five pieces and detonate each separately with a fuse.

It has been determined that about 5 per cent of water is the maximum content for unconfined guncotton capable of detonation by a Du Pont No. 30 fuse.

Priming charges are not to be prepared until just previous to the time they are to be used in loading. When the primers have been dried, they should be kept in well-sealed jars unless they are to be used very soon after drying, in which case they will be stored in assembled fuse cans; when thus stored the assembled fuse cans should be kept in a cool, dry, and secure room away from other explosives. If, however, the primers are to be stored for any length of time, two strips of blue litmus paper are inserted between the cakes, which are inspected from time to time. If the litmus paper shows decided redness, it should be removed and fresh strips inserted. If these strips turn red in a few hours, the primers should be thoroughly wet with fresh water. In general, the period of storage will be short and no particular examination of the dry guncotton will be required.

Dry guncotton should be handled as little as possible, to prevent crumbling and scattering of guncotton dust. Finely divided guncotton is difficult to remove by brushing and if allowed to collect about a room may give serious trouble by flashing should a portion become ignited. This dust may be removed with a damp sponge or cloth.

Dry guncotton which is not used as contemplated shall be rewet with the proper amount of water and repacked.

Samples of each lot of guncotton issued to the service are preserved in the laboratory of the Ordnance Department for chemical test. These retained samples are subjected regularly to technical inspection and test by that department to determine their condition as to stability. This will insure the detection of lots that are deteriorating and their removal from the posts or their destruction before they have deteriorated to such an extent that they become dangerous.

=Dynamite.=—Dynamite cartridges are packed ordinarily in sawdust in wooden boxes. Each cartridge is wrapped in paraffin paper. The cartridges are arranged in the box so that when they are transported all cartridges will lie on their sides and never on their ends. Usually the amount of explosive in a single package will not exceed 50 pounds.

The boxes must never be allowed to stand so that the cartridges will be vertical.

Like other nitroglycerin, dynamite freezes at about 40° F., and in its frozen condition is, under ordinary circumstances, less liable to explosion from detonation or percussion than when thawed, but more susceptible to explosion by simple ignition. Should any of the nitroglycerin be exuded, the dynamite cartridges are much more sensitive to explosion by a blow.

It is important that dynamite cartridges be kept dry. If exposed to a moist atmosphere, there is a tendency of the water, condensed from the air on all exposed surfaces, to displace the nitroglycerin.

The cases should be raised from the floor on skids and the floor underneath covered with clean sawdust. The sawdust should be removed from time to time, the old sawdust being burned in the open air.

Rubber gloves should be worn in handling this explosive, or in the absence of rubber gloves cover the hands with grease and wear cotton gloves. This is for the protection of the skin from the injurious effect of nitroglycerin.

Dynamite may be stored with wet guncotton, explosive D, and trotol.

Date of receipt at post shall be marked on each box.

The priming charge for dynamite is a pound of loose dynamite contained in a small bag which fits easily into the fuse can. In filling the bag rubber gloves must be worn. To insert the fuses the bag is opened and the fuses embedded in the explosive, the choke being tied around the fuse wires.

At the monthly inspection all boxes shall be examined to see if they are dry. If not dry, all shall be exposed to the dry air out of the direct rays of the sun.

The principal source of danger from dynamite is in the exudation of the nitroglycerin. Exudation is indicated by the presence of small white, oily, lustrous globules of liquid, either among the particles of dynamite or on the packages. If such globules are discovered, they may be identified positively as nitroglycerin by absorbing a drop in a piece of unglazed paper, which should be placed on an anvil or other piece of metal, and striking it a sharp blow with a hammer. If it be nitroglycerin, an explosion will occur. Another test is to set fire to the paper, and if the liquid be nitroglycerin it will burn with a crackling noise and a greenish-yellow flame.

If exuded nitroglycerin has stained floors or other material not readily destroyed, the nitroglycerin may be decomposed and rendered harmless by washing with “sulphur solution.” This solution may be made by boiling 50 pounds of lime in a barrel of water and adding powdered sulphur until the solution will take up no more. This will require about 20 pounds of sulphur. The resulting bright orange-colored solution should be filtered and only the filtrate used. A suitable filter for this purpose is a piece of thin cheese-cloth. Sodium carbonate may be used in the place of lime.

Dynamite may be destroyed by burning in small quantities at a time. Slit the cartridge with a knife, spread out the contents over some straw or shavings, and ignite carefully. Do not attempt to burn frozen dynamite.

=Mine fuses.=—These are regular commercial electric fuses, extra quality, and each contains about 25 grains of mercury fulminate. Fuses are supplied in pasteboard boxes containing 50 each, pasteboard boxes being shipped in suitable wooden boxes. They are supplied with long leads which are cut to proper length when the mines are loaded. _They must not be stored with other explosives._

=Loading mines.=—In loading mines the following precautions are observed:

(_a_) Funnels are used to cover the screw threads. (_b_) Trotol is poured through the funnels. (_c_) Cakes of guncotton or packages of dynamite are passed through the funnels by hand. (_d_) The screw threads are wiped carefully before the compound plug is inserted. (_e_) Pieces of canvas or paulins should be spread upon the floor of the loading room. After the loading has been completed the canvas should be removed and thoroughly cleaned. The floor of the loading room should be scrubbed and all refuse destroyed.

=Unloading mines.=—Mines charged with trotol or wet guncotton may be unloaded without danger; the compound plug being unscrewed, the cakes of wet guncotton are removed by hand, repacked in the original boxes, a little fresh water added, and the boxes closed. If loaded with trotol, the charge is poured out into the boxes, which are then closed. Trotol should be inspected carefully when removed from the case, and if there is indication that any of it has undergone a change while the mine was loaded, a report should be made to the War Department.

In unloading mines charged with dynamite too many precautions can not be taken. The mine should be held either in an opening in a raft or behind an earthen traverse and the compound plug removed by some arrangement which may be operated from a safe distance. If the mine has been planted for some time the recovered dynamite is usually destroyed. Sometimes the interior of the mine case may be found coated with an extremely thin film of exuded nitroglycerin. This film may be destroyed by filling and thoroughly rinsing the case with “sulphur solution.”

APPENDIX NO. 2.

THE HORNSBY-AKROYD OIL ENGINE AND GENERATOR.

(See also Artillery Notes, No. 12.)

=The engine.=—This is a horizontal, single-acting, single-cylinder kerosene engine, having a flyball governor and operating on a four-stroke cycle. This cycle consists in turn of the explosion on the first outstroke, the expulsion of the products of the explosion on the following instroke, the intake into the cylinder of a mixture of air and oil vapor on the following outstroke, and the compression of this explosive mixture on the next instroke. This cycle therefore requires two complete revolutions of the crank shaft for one complete set of operations.

On one side of the cylinder near the closed end is a valve box containing two valves, the air-inlet valve and the exhaust valve. The air-inlet and the exhaust valves are actuated by separate levers, each lever being moved by a cam mounted on a horizontal shaft, driven by the crank shaft through worm gearing. This horizontal shaft makes but one revolution while the crank shaft makes two; thus the air-inlet and the exhaust valves are each opened once every two revolutions of the flywheel.

At the back of the cylinder, in prolongation of its axis, is a cast-iron box called the vaporizer, which is always open to the cylinder. Before starting the engine this vaporizer must be heated by an external lamp, so that it will vaporize the oil when it is first pumped into it. After the engine has started running, the lamp is no longer required, as the vaporizer is kept at a sufficient heat by the internal explosions.

A small oil pump, worked by the air-valve lever, draws oil from the oil tank under the engine and forces it into the vaporizer at the proper time. The oil, on its way from the pump to the vaporizer, passes through a valve box attached to the vaporizer; this valve box has two valves in it, a horizontal one, kept closed by a spring which the oil forces open as it goes into the vaporizer; the other, a vertical one, also kept closed by a spring. Should the engine run too fast, the governor opens this latter valve and allows some of the oil to flow back to the oil tank through the waste pipe. This valve can also be opened by turning the little regulating handle, which will stop the supply of oil to the vaporizer and thus stop the engine.

INSTRUCTIONS FOR WORKING.

=Frosty weather.=—If there is danger of freezing, on shutting down drain the water from the circulating pipes and cylinder jacket, and valve box if water-jacketed; otherwise they may burst or crack.

=Caution.=—Before starting, see that the cocks which admit water to the water jacket of the vaporizer valve box are open; that the cock on the main water pipe from the bottom of the water tank is open; that the water in the tank is above the upper circulating pipe; that the drain cock is closed; and that the oil tank is filled with kerosene. _Gasoline must not be used with this engine._

=Heating the vaporizer.=—Open the relief cock on top of the engine cylinder. Place the lamp on the stand under the vaporizer; fill the lamp with oil by means of the filling pipe till the oil is 1 inch below the pipe; and put a piece of wick into the cups which are formed around the pipes. These wicks, which should consist of a piece of ordinary asbestos packing, will last for several weeks. Place the lid of the vaporizer cover crosswise on the cover to allow the escape of heated gas and air.

A little alcohol or kerosene should be poured into the cup under the coil and lighted. The cups may be filled with kerosene by closing the air-escape valve and working the air pump. The pressure forces oil out through the vapor nozzle and it will run down into the cups. When this is nearly burned out pump up the reservoir with air by the air pump. Oil will issue from the small nozzle and give a clear flame. When it is desired to stop the lamp, turn the thumbscrew on the reservoir filling nozzle to let the air out. Should the nozzle become choked it should be cleaned with the small needles for that purpose.

The heating of the vaporizer is one of the most important things to be attended to, and care must be taken that it is hot enough at starting. The attendant must see that the lamp is burning properly and that a good clear flame is given off for from 5 to 10 minutes, according to the size of the engine. If, however, the lamp is burning badly, it may take longer to become heated sufficiently. It is important that this should be carefully attended to, for though the engine may start, if the vaporizer is not as hot as it should be the engine will run badly and perhaps soon stop altogether. Failures of engines to run properly can in most cases be traced to this source.

No time should be lost in starting the engine after the vaporizer has been sufficiently heated, as the engine may not run satisfactorily if the vaporizer is allowed to cool after heating it. The lamp should be left burning a few minutes after starting.

=Oiling the engine.=—Oiling the engine should always be done during the heating-up of the vaporizer.

See that the oil cups on the two main crank shaft bearings are fitted with proper wicks and filled with oil. Adjust the lubricator on the large end of the connecting-rod and oil the small end which is inside the piston.

Oil also the following: The bearings on the horizontal shaft and the skew gearing, the rollers at the ends of the valve levers and their pins, the pins on which the levers rock, the governor spindles and joints and the bevel wheels which drive the same, and the joints that connect the governor to the vertical valve of the overflow. For such bearings none but the best engine oil should be used.

It is necessary that a suitable oil should be used for lubricating the cylinder, and unless such an oil be used for this purpose the engine may run badly and perhaps stop altogether. Under no circumstances must a thick cylinder oil be used, and the oil must not be used over again on the piston. Do not use ordinary lubricating oil. A high-grade gas-engine oil especially suited to this engine should be used and the piston should be kept flooded with it.

=Starting the engine.=—Throw the hand lever to “To start.” Turn the small crutch-handle regulator Y to the position “Shut” and work the pump lever up and down until oil is seen to pass the overflow freely. Turn the regulator back to “Open,” work the pump lever up and down a few strokes. Vapor should issue with some force from the relief cock on the cylinder. This indicates sufficient heat. Close the relief cock and pump a few strokes. Man the flywheel and start the flywheel backward, using the weight of the body if necessary, bringing the piston up against compression as sharply as possible, and then release the wheel, when an explosion should take place and the engine start forward. As soon as the engine has sufficient speed to carry it past a full compression, throw the lever to “To work.” When full speed is obtained, cut down the pump stroke to correspond to the load, open the oil feeders, and go over the engine carefully, seeing that the cylinder oil feed is working.

=Oil pump.=—When the cylinder is working at its full power the distance between the round flanges on the pump plunger should be such that the hand gauge (supplied with the engine, and to be found in the tool box) will allow the part stamped “1” just to fit in between the flanges; if at any time the positions of these flanges be altered they can be readjusted to this gauge. The other lengths on the hand gauge are useful for adjusting the pump to economize oil. When running on a medium load, use length marked 2; on a light load, use length marked 3. See that the pump packing is not too tight.

=Running the engine light.=—When the engine is to run light—that is, with no load or with a light load—it is best to alter the stroke of the pump to the amount of oil that will keep the engine running. This amount can be reduced so that the speed of the engine is a few revolutions under the normal, which will allow the vaporizer to get a small charge each time and keep it from cooling. The cock on the return of the water circulating pipe may be nearly closed to keep the cylinder warmer. These remarks do not apply when the load is intermittent and the engine is running light for a short time only.

=Air-inlet and exhaust valves.=—See that the air-inlet and the exhaust valves are always working properly and drop onto their seats. They can at any time, if required, be made tight by grinding with a little flour of emery and oil.

To insure a good seat to the valves when the stems are expanded by heat the stems should clear the set-screws on the levers at least ¹/₁₆ inch when the air and the exhaust levers are clear of the cams. A greater clearance is undesirable, as it prevents the full opening of the valves.

If at any time the air-inlet or the exhaust valves appear to be opening or closing at the wrong time, take off the nut on the end of the lay shaft which holds the skew-wheel on and see that the chisel cuts on the shaft are opposite to one another. The lay shaft is coned where the skew wheel is fixed on and it is held on simply by friction, the nut being tightened against it.

Should it at any time become necessary to take out the crank shaft, always be sure that the skew-wheel gearing is put together so that the tooth marked “0” on the crank shaft skew-wheel fits in between the two teeth marked “0” on the oil-shaft skew-wheel.

=Vaporizer valve box and pipes attached to vaporizer.=—In this box there are two valves. The vertical one is regulated by the governor, and when the engine runs faster than its proper speed the governor pushes it down, thus opening it and allowing some oil to return to the oil tank. The horizontal valve in this box is a back-pressure valve. If at any time this valve is not working properly, vapor will be seen coming out of the overflow pipe; in this case the valve should be examined. By screwing off the outside cap the tail of this valve can be seen; if the valve is turned around a few times it will probably dislodge any dirt that may be under it; if, however, this does not stop the leakage the valve should be taken out for inspection.

If the horizontal valve and sleeves are taken out at any time, great care must be taken in replacing them to use the same thickness of jointing material as before or the distance the valve opens will be altered.

See that the pipe from the pump to the vaporizer valve box is inclined upward all the way from the pump. If this is not so, an air pocket will be formed in which a certain amount of air will be compressed upon each stroke of the pump. This will cause the oil to flow in slowly and not suddenly as it should. If the oil tank be emptied of oil at any time, air will get into the suction and delivery pipes of the pump and it will take some time before the oil going through the pump and pipes will be free of this air; for awhile thereafter, the engine will not work properly, as the air, by being compressed as the pump works, will interfere with oil being pumped in suddenly. It is best, if the oil gets below the filter in the tank, to work the pump by hand for about 10 minutes, holding the relief valve (on the vaporizer box) so as to get air well out of the pipes.

=To stop the engine.=—Turn the crutch-handle regulator to “Shut.” Close the automatic lubricator. If it is desired to stop the engine for a short time only, put the lamp back under the vaporizer to keep it hot.

=Setting the oil engine and the generator.=—The engine and generator should be so located that the distance from center to center of pulleys should be as nearly correct as possible when the generator is at the middle point of the base rails, so that the proper tension of the belt may be obtained within the limits of adjustment allowed by the rails.

The two pulleys should be accurately in line and the belt not too tight. The generator base should rest on a wooden frame to separate it from the concrete pier. Both engine and generator should be held firmly in position by anchor bolts.

For the generator bearings a quantity of the best dynamo oil is furnished; the commutator should be clean and smooth, and the brushes should fit the surface. The commutator should be cleaned occasionally with a little paraffin on canvas, and the brushes should be adjusted, so that when running at full load no sparking occurs.

All electrical connections should be firmly made and kept thoroughly clean. A cover should be kept on the generator when not in use. If the machine be damp it should be allowed to dry before running at full load.

=NOTE.=—A few new installations have been supplied with 5-kw. gasoline electric sets, and future installations will be similarly equipped. Wherever installed, pamphlets on the care and operation of the gasoline sets have been furnished, containing full instructions for the guidance of those concerned.

APPENDIX NO. 3.

THE STORAGE BATTERY.

(See pamphlets issued by the Electric Storage Battery Co., Philadelphia, Pa., on General Instructions for the Operation and Care of the Chloride Accumulator.)

=Unpacking material.=—Great care should be taken in the unpacking and subsequent handling of the various parts of the battery, as many of them are easily broken or bent out of shape by rough handling.

Open the crates or packing boxes on the side marked “Up” and carefully lift contents out; never slide them out by turning the crate on its side.

Upon opening the crates and boxes, carefully count the contents of each package, and check with the shipping list. A number of small parts will usually be found in each shipment, and care should be taken to examine the packing materials to determine that no parts have been overlooked.

Immediately upon opening the crates the materials should be carefully examined for breakage. Cracked jars, whether of glass or rubber, should not be set up, for if put into use leakage of electrolyte may cause annoyance or trouble.

=Location of battery room.=—The proper location of the battery is important. It should be in a separate room, which should be well ventilated, dry, and of moderate temperature. Extremes of temperature affect the proper working of a battery. The air should be dry, for if damp there is danger of leakage due to grounds.

The ventilation should be free, not only to insure dryness, but to prevent chance of an explosion, as the gases given off during charge form an explosive mixture if confined. For this reason never bring an exposed flame near the battery when it is gassing.

Direct sunlight should not fall on the cells.

The trays, the benches on which the cells rest, and all metal work (iron and copper) should be painted with asphaltum varnish.

=Assembling and placing cells in position.=—Place the jars, after they have been cleaned, in position on the stands, which should be provided for the purpose and which should be so situated in the room that each cell will be easily accessible. The jars are set in the trays, which previously should be filled with fine dry sand even with the top, the trays resting on the glass insulators.

Place the elements as they come from the packing cases on a convenient stand or table (the elements are packed positive and negative plates together; the positive has plates of a brownish color, the negative of a light gray—the negative always has one more plate than the positive), cut the strings that bind them together, and carefully pull the positive and negative groups apart, throwing the packing aside. After carefully looking over both groups and removing any dirt or other foreign matter, assemble them, with separators between each positive and negative plate.

When putting into the jars be careful that the direction of the lugs is relatively the same in each case, thus causing a positive lug of one cell always to connect with a negative of the adjoining one, and vice versa. This insures the proper polarity throughout the battery, bringing a positive lug at one free end and a negative at the other.

Before bolting or clamping the lugs together, they should be well scraped at the point of contact to insure good conductivity and low resistance of the circuit; this should be done before the elements are taken apart and directly after unpacking, if the battery is to be set up at once. The connections should be gone over and tightened several times after the lugs are first fastened together to insure good contact.

=Connecting up the charging circuit.=—Before putting the electrolyte into the cells, the circuits connecting the battery with the charging source must be complete, care being taken to have the positive pole of the charging source connected with the positive end of the battery.

=Electrolyte.=—The electrolyte is dilute sulphuric acid of a specific gravity of 1.210 or 25° Baumé, as shown on the hydrometer at temperature of 70° F.

The electrolyte should cover the top of the plates by one-half inch to three-fourths inch, and must be cool when poured into the cells. The jars should be numbered with asphaltum varnish and a line made with the same material to indicate the height at which the electrolyte should be kept.

=Initial charge.=—The charge should be started at the normal rate as soon as the electrolyte is in the cells and continued at the same rate, provided the temperature of the electrolyte is well below 100° F., until there is no further rise or increase in either the voltage or specific gravity over a period of 10 hours, and gas is being given off freely from all the plates. Also, the color of the positive plates should be a dark brown or chocolate and that of the negatives a light neutral gray. The temperature of the electrolyte should be closely watched and, if it approaches 100° F., the charging rate must be reduced or the charge stopped entirely until the temperature stops rising. From 45 to 55 hours at the normal rate will be required to complete the charge; but if the rate is less, the time will be proportionately increased. The specific gravity will fall rapidly after the electrolyte is added to the cells, and may continue to fall for some time after charging begins. It will finally rise as the charge progresses, until it is again up to 1.210 or possibly slightly higher. The voltage for each cell at the end of charge will be between 2.5 and 2.7 volts, and for this reason a fixed or definite voltage should not be aimed for. It is of the utmost importance that this charge be complete in every respect.

At the end of the first charge it is well to discharge the battery about one-half and then immediately recharge it. Repeat this treatment two or three times and the battery will be in proper working condition.

After the completion of a charge (initial or with the battery in regular service) and the current off, the voltage will fall immediately to about 2.20 volts per cell, and then to 2 volts when the discharge is started. If the discharge is not begun at once, then the pressure will fall quite rapidly to about 2.05 volts per cell, and there remain while the battery is on open circuit.

=Battery in regular service.=—A battery must not be repeatedly overcharged, undercharged, overdischarged or allowed to stand completely discharged. After the initial charge is completed, the battery is ready to be put into regular service.

A cell should be selected as a “pilot cell”; that is, one that is in good condition and representative of the general condition of the battery. The height of the electrolyte in this cell must be kept constant by adding a small quantity of water each day. This cell is to be used particularly in following the charge and indicating when it should be stopped.

When the battery is in regular service, the discharge should not be carried below 1.75 volts per cell at full load. Standing completely discharged will cause permanent injury; therefore the battery should be immediately recharged after a heavy discharge.

In usual service, with the normal rate, it is advisable to stop the discharge at 1.90 volts per cell. If the discharge rate is considerably less than normal, the voltage should not be allowed to fall as low as 1.90 volts per cell, for the reason that with a very low rate of discharge the voltage will not begin to fall off until the limit of capacity is almost reached. The fall in specific gravity of the electrolyte also serves as an indication of the amount taken out and is in direct proportion to the ampere-hour discharge, thereby differing from the drop in voltage, which varies irregularly for different rates and degrees of discharge. For this reason, under ordinary conditions, the fall in specific gravity is to be preferred in determining the amount of discharge.

The actual amount of variation in the specific gravity of the electrolyte between a condition of full charge and a complete discharge is dependent upon the quantity of solution in the containing vessel compared with the bulk of the plates. When cells are equipped with the full number of plates, the range will be about 35 points (0.035 sp. gr.); for instance, if the maximum specific gravity reached on the preceding overcharge is 1.209, the extreme limit beyond which the discharge should not be carried is about 1.174. If the cells have less than the full number of plates, this range in specific gravity is proportionately reduced, except in the case of the “pilot cell,” which should be equipped with a device for displacing the excess electrolyte.

The available capacity is temporarily reduced at low temperatures; with a return to normal temperature the capacity is regained.

The battery should preferably be charged at the normal rate. It is important that it should be sufficiently charged, but the charge should not be repeatedly continued beyond that point. Both from the standpoint of efficiency and life of the plates the best practice is the method which embraces what may be called a regular charge, to be given when the battery is from one-half to two-thirds discharged, and an overcharge to be given weekly if it is necessary to charge daily, or once every two weeks if the regular charge is not given so often.

The regular charge should be continued until the specific gravity of the pilot cells has risen to within five points of the maximum, as shown on the last previous overcharge. For example, if on the previous overcharge the maximum is 1.210, then on the following regular charges the current should be cut off when the specific gravity of the pilot cell reaches 1.205. The pilot cell method of noting the end of charge should not be used with a battery unless all the cells are approximately in the same condition. With an old battery whose plates are not uniform, readings should be taken on each cell to determine the end of charge.

The overcharge should be prolonged until all the cells gas freely and until no rise in the specific gravity and voltage of the pilot cell is shown for five successive 15-minute readings.

Just before the overcharge the cells should be carefully examined to see that they are free from short circuits. If any short circuits are found they should be removed with a stick or a piece of hard rubber; do not use metal.

As the temperature affects the specific gravity this must be considered and correction made for any change of temperature. The temperature correction is one point (0.001 sp. g.) for 3 degrees change in temperature. For instance, electrolyte, which is 1.210 at 70°, will be 1.213 at 61° and 1.207 at 79°.

=Inspection.=—In order that the battery may continue in the best condition it is essential that specific gravity and voltage readings be taken on all cells in the battery at least once a week; the specific gravity readings on the day before the overcharge and the voltage reading near the end; the voltage readings must always be taken when the current is flowing, open circuit readings being of no value. Also, at the end of each charge it should be noted that all of the cells are gassing moderately and at the end of the overcharge very freely.

=Unevenness of cells; cause and remedy.=—If any of the cells should read low at either time and do not gas freely with the others at the end of charge, examine them carefully for pieces of scale or foreign matter which may have lodged between the plates. If any are noted, remove them by pushing down into the bottom of the jar with a strip of wood. Never use metal of any kind for this purpose.

If, after the cause of the trouble has been removed, the readings do not come up at the end of the overcharge, then the cell must be cut out of circuit on the discharge, to be cut in again just before beginning the next charge, during which it should come up all right.

Impurities in the electrolyte will cause a cell to work irregularly and the plates to deteriorate. Should it be known that any impurity has gotten into the electrolyte, steps should be taken to remove it at once. The solution should be replaced with new immediately, thoroughly flushing the cell with water before putting in the new electrolyte. The change should be made when the battery is discharged, for the impurities will be in the electrolyte when the battery is discharged. Immediately after the change the cell should be charged. If in doubt as to whether the electrolyte contains impurities, a half-pint sample, taken at the end of discharge, should be submitted for test.

=Sediment.=—The accumulation of sediment in the bottom of the jars must be watched and not allowed under any circumstances to get up to the plates; if this occurs, rapid deterioration will result. To remove the sediment, the simplest way, if the cells are small, is to lift the elements out after the battery has been fully charged, draw off the electrolyte, and then dump the sediment, and clean the jar with water, getting the elements back and covered with electrolyte again as quickly as possible, so that there will be no chance of the plates drying out. Electrolyte, not water, will be required to complete the filling of the cells, the specific gravity being adjusted to standard (1.210 at the end of charge).

=Evaporation.=—Do not allow the surface of the electrolyte to get down to the top of the plates; keep it at its proper level (one-half inch to three-fourths inch above the top of the plates) by the addition of pure water, which should be added at the beginning of a charge, preferably the overcharge. It will not be necessary to add electrolyte except at long intervals or when cleaning, as noted above. Electrolyte added to replace loss should be of specific gravity 1.210.

=Battery used but occasionally.=—If the battery is to be used at infrequent periods, it should be given a “freshening” charge every two weeks.

=Putting the battery out of commission.=—If it is thought best to put the battery out of commission for a time, then it must be treated as follows: After thoroughly charging, syphon off the electrolyte (which may be used again) into convenient receptacles, preferably carboys which have been previously cleaned and have never been used for other kinds of acid, and as each cell becomes empty immediately fill it with fresh, pure water. When water is in all the cells allow them to stand 12 to 15 hours, then draw off the water; the battery may then stand without further attention until it is again to be put into service; then proceed as in the case of the initial charge, as described above.

If for any reason any cell becomes discharged before the others, it should be cut out on discharge and worked up to normal before being used.

Should the battery sulphate, charge and discharge frequently, not using less than one-half normal rate at any time and increasing to full rate as the plates show signs of recuperation; keep the temperature of the cells below 100° F. Frequent exercise will clear the plates in a badly sulphated battery.

Keep careful records of all charging voltages, specific gravities, and troubles with the cells.

The following is a recapitulation of the important points in operating a storage battery:

CONDENSED INSTRUCTIONS.

1. Excessive charging must be avoided. A battery should not be undercharged, overdischarged, or allowed to stand completely discharged.

2. Keep the electrolyte at the proper height above the top of the plates.

3. The daily and weekly readings should be regularly and accurately taken and recorded.

4. Inspect each cell of the battery carefully at regular intervals.

5. If any low cells develop do not delay in bringing them back to condition.

6. Do not allow the sediment to get up to the plates.

7. Do not allow impurities, either solid or liquid, to get into or remain in the cells.

8. Have the battery room well ventilated, especially while charging.

9. Never bring an exposed flame into the battery room during or shortly after the gassing period of a charge.

10. Keep the floor and other parts of the battery room clean and dry.

11. Keep the iron, copper, or other metal work about the battery room free from corrosion.

12. Keep all connections clean and tight.

13. Post a copy of these condensed instructions in a conspicuous place.

APPENDIX NO. 4.

SUBMARINE MINE CABLE.

Submarine mine cable is shipped on reels having an outer sheathing for protection in transit, with at least 12 feet of both ends of the cable brought out and coiled on the head of the reel for test purposes. If the cable is not for immediate use, it should be moved to the cable tank, and by means of the overhead trolley and cable tongs put in its position in the tank, the two ends being properly tagged and firmly fixed so as to allow it to be tested. In arranging the multiple cable in the tanks that which is to be used first should be most readily accessible.

The cable tank should be provided with a cover to keep it clean, as well as to lessen as much as possible variations of temperature. Enough clean water to cover by several inches the outer sheathing of the cable reels should be kept in the tanks, but in climates where the water in the cable tanks would normally freeze to a depth exceeding 2 feet, the water should be let out of the tanks before ice begins to form and not again admitted until the following spring. In localities where the tanks may become a breeding place for mosquitoes, as a preventive measure, salt water from the ocean or bay should, when practicable, be used for filling the tanks, or where it is necessary to use fresh water sufficient salt should be added to produce a 3 per cent solution. No oil or kerosene should be used in the tanks.

The methods of recording tests and of classifying and transferring submarine mine cable are prescribed by orders from the War Department. The tests of submarine mine cable at posts will consist in determining the insulation and conductor resistances.

The insulation surrounding the conductor of a cable is supposed to be uniform in regard to quality of material, density, and thickness. The resistance which it offers to the passage of a current through it will then vary inversely with its length. In comparison the insulation resistance of 1 mile of cable is taken as the standard. This insulation has a large negative temperature coefficient; that is, an increase of temperature lowers its resistance. It is customary to reduce all insulation resistance to that at a standard temperature of 60° F., and for this purpose reduction factors applicable to the particular insulation compound should be furnished with the cable. (Note: It has been found that for most compounds, if the logarithms of the resistance are plotted as ordinates against the temperature in degrees F. as abscissæ, the resulting curve will be very nearly a straight line.)

The ordinary methods of measuring resistance—that is, by means of a Wheatstone bridge, or by fall of potential, or by voltmeter—can not be used in measuring resistance as high as that of the insulation of a submarine cable. For this the direct deflection method is employed.

In brief, this consists of the following steps:

First. The deflection produced in a galvanometer by a current from a battery through a known resistance, usually 100,000 ohms, is determined, whence is calculated the resistance through which this same battery would produce a deflection of one point using the unity shunt. This is expressed in megohms and is called the galvanometer “constant” under the conditions.

Second. The deflection produced by the current from the same battery through the insulation of the cable is determined, whence, from “First,” the corresponding number of megohms is calculated.

Third. This multiplied by the length of the cable in miles and corrected for temperature gives the required insulation resistance per mile.

This testing can be made most satisfactorily on dry days, but a close adherence to the instructions herein given relative to the preparation of the cable ends, the insulation of the cable lead and of the battery, and the drying out of the test room and instruments should enable satisfactory work to be done under adverse conditions of weather or climate. The following apparatus is required: Reflecting galvanometer, universal shunt, special testing key, 100,000-ohm resistance box, battery of dry cells giving approximately 100 volts, and stop watch.

Figure 16 shows diagrammatically the arrangement of the apparatus for testing a reel of cable. As a rule the instruments should be so placed that one person may manipulate the key and the shunt while at the same time observing the galvanometer.

The 100,000-ohm box, as a protection to the galvanometer in testing, is always kept in the circuit and its value should be subtracted from the resistance determined, except in the case of high insulation resistance when it will not be necessary to make the subtraction.

The universal shunt is always employed with the galvanometer and is used both to vary the current through the latter and to protect it from a violent throw at the instant of making or breaking the circuit at the testing key. This last is accomplished by having the shunt on zero at such times.

The galvanometer being a very sensitive instrument must be solidly supported so as to be free from jars or vibrations.

The special testing key, shown diagrammatically in the figure, has its binding posts plainly marked. It is a double-throw key and has two positions upon each side. When completely closed to the right, the cable is charged through the galvanometer from the positive pole; when to the left, from the negative pole of the battery. In each case the deflection of the galvanometer is in the same direction. When partly closed on either side, the cable is discharged to earth through the galvanometer. (Note: It will be observed that the connections are such that the galvanometer is always connected to the cable core and never to the ground. With this connection, _so long as the lead PX is free from leaks or grounds_, the galvanometer measures only the current actually passing through the core and not that leaking through any imperfect insulation in the battery and leads.)

Cable testing is a very simple operation, but extreme care is necessary in all operations.

[Illustration: FIG. 16.—CABLE TESTING.]

The following is a detailed description:

=I. Preparing the cable for testing.=—1. Closely examine each conductor end. Look particularly for unusually hard or brittle insulation and for torn, pinched, or punctured insulation, especially near the ends of the armor wires. If any of the ends are not in perfect condition, cut off enough cable to secure good ends. (_Caution._—Do not cut off more than enough to secure good ends, for after three or four tests it may be necessary to unreel the whole cable to secure enough of the inner end above water.)

2. Verify the tagging. Remember that the “shore end” is the end from the outer coils on the reel and is numbered clockwise. The other end is numbered contraclockwise.

3. The “ground” should be made by taking several turns of bare copper wire around the armor of the cable to be tested and soldering them in position. One such ground in each tank is sufficient. Whenever “ground” or “earth” is subsequently spoken of, this ground in the tank is meant, and not a connection to ground at some point outside the tank.

4. The leads PX and BY (fig. 16) should be of loading or other heavily insulated wire. They must be carefully insulated from each other, from the ground, and from the walls or other parts of buildings. This is especially true of the cable lead PX. In damp weather porcelain-knob insulators and porcelain tubes (the latter for use in passing through walls or partitions) may not be sufficient to afford proper insulation for the cable lead. In such case the latter should be suspended _in the air_ from the testing switch to the cable tank by means of several chains of paraffined porcelain insulators suspended by marline or protective tape which has been boiled in paraffin. These suspensions should be in each case under cover and should be kept as dry as possible. The length of the leads is immaterial. If loading wire is used, the distance between supports should be short (not over 50 feet), as this wire stretches considerably from its own weight, pulling out the insulation and giving a very thin wall, particularly at points of support. Extreme care should be taken to tighten up on the knob insulators, in case they are used, just enough to hold the wire without pinching the insulation.

5. Using a double connector, join the lead BY to the ground wire on the cable above the surface of the water. Put a connector on the end of the other lead so that it can be readily attached in turn to each conductor.

6. Any protective covering, such as armor, jute, etc., should be removed from the ends of the conductors for a distance of about 12 inches, thus laying the insulation coating bare. This latter should not be handled and must be kept scrupulously clean. With a _clean dry_ knife prepare each conductor of the cable to be tested by cutting off about 1 inch of the insulation from each end of the wire and then tapering the end of the insulation for about 1 inch, leaving a perfectly clean surface. In damp weather dip each end of each conductor into melted paraffin (not boiling, but heated above 212° F.). Secure one end of the cable so that it is well separated from the surrounding objects and separate the conductors so that no ends are touching.

7. Take one strand of a loading wire about 4 feet long and wrap it two or three times around the projecting copper end of each conductor at the other end of the cable, then connect it to earth. See that the conductors at this end are dry. Leave the lead PX disconnected and suspended in the air.

=II. Setting up the testing apparatus.=—1. Select a light, dry room as near the cable tank as practicable.

2. Use dry cells for the battery. The voltage of the battery should be such as to give a full scale deflection of the galvanometer through the resistance employed for taking the constant (with shunt at ¹/₁₀₀₀). Large galvanometer throws are essential for reliable results.

Set up the cells on shelves in a small closed closet or box, with narrow strips of wood or heavy cardboard laid between each row of cells, lengthwise and crosswise. The height of each strip should be about half the height of a cell, so that the two layers of strips will come nearly to the tops of the cells and keep them well separated. Wire the cells in series and bring the terminals out to a double-pole single-throw switch, which should be on a heavy porcelain or slate base and rated for at least 250 volts. (It may be found desirable to install some electric lamps in the closet to keep the battery dry.)

If difficulty is experienced in eliminating grounds from the battery set up in this manner, the battery box should be suspended in air by means of chains of paraffined cleats.

3. Set up the galvanometer on a pier or on a window sill if the building is of masonry. It should be insulated by placing its feet on a slate or ebonite slab, or in glass insulators. Remove the cover. Adjust the level until the suspended coil hangs freely. Maneuver the suspended coil, by means of the knob at the top of the tube, until its face is parallel with the face of the instrument. Then adjust the level until the upper suspension hangs in the center of the supporting tube, and the air gap between the coil and armature is symmetrical. Replace the cover. Put on the scale and the telescope. Turn the mirror so that it reflects the 0 of the scale approximately, getting exact adjustment by moving the scale. Be careful (particularly in dry weather) not to touch the glass of the cover or to do anything which will produce a static charge on the glass.

The galvanometer scales are usually graduated in equal divisions corresponding to 1 millimeter on the circumference of a circle whose radius is 1 meter. Each tenth division is usually marked with a number. This number is sometimes 1 instead of 10, 2 instead of 20, and so on. The number of divisions to read and record is the number of smallest (millimeter) divisions. Do not try to read closer than ½ of one division. The larger the throw the less the personal error. No accurate conclusion can be drawn from a very small throw.

4. Place a table or low shelf conveniently to one side and place the shunt, the testing key, the ⅒ megohm box, and a voltmeter on it. The apparatus should be insulated by an ebonite or slate slab, or glass insulators. Fasten the shunt and the key securely to the table or the shelf. (The use of paraffin paper for insulating instruments is a makeshift at best. It soon gets soiled and creased, then it has to be replaced.)

The use of lamps to keep the apparatus dry may be desirable, or it may be found convenient to expose the apparatus to the sun for a few minutes before beginning the test on any day. The use in the testing room of a small stove or of a gasoline torch for two or three hours before the beginning of the testing will ordinarily prove very advantageous.

5. Wire up as in figure 16, except that the leads from the testing key should be carried to the battery through the double-pole single-throw switch above referred to. (The battery switch should be opened whenever any connections are made or altered.) All leads used in connecting up the instruments should be of heavy copper, and stiff enough to hold permanently any shape to which they are bent. They should be supported at points of connection only, and should not lie on the table or within an inch of each other.

=III. Testing the insulation of the apparatus.=—1. _Voltmeter test of battery insulation._—This is a rough test, but should be included. A serious ground can be much more quickly located with a voltmeter than with the galvanometer.

(_a_) Disconnect the battery leads at the battery switch; connect + lead of battery to + post of the voltmeter; connect the B end of the lead BY to - post of the voltmeter; - lead of the battery should be in the air. Close the voltmeter switch and read.

(_b_) Disconnect the voltmeter. Connect - lead of the battery to - post of the voltmeter. Connect the B end of the lead BY to + post of the voltmeter; + lead of the battery should be in the air. Close the voltmeter switch and read.

If any deflection is obtained in either case, the battery or its connections are grounded. Locate and remove the ground. (See Foster or some other practical handbook.)

2. _Testing the battery voltage._—Connect the voltmeter across the battery terminals. Read and record the voltage. (If there is no voltmeter available which will read as high as the battery voltage, take the voltage of the battery in sections and add, or make a multiplier of one of the resistance coils in the ⅒ megohm box.)

3. _Testing the battery and the apparatus for grounds with the galvanometer._—With a camel’s-hair brush go over all the instruments and carefully remove dust. See that the instruments and connections are dry. Do not blow on the instruments.

Open the battery switch. Connect the battery leads to the battery switch. Disconnect lead PX at P and connect the earth leads BY and EY to the key at “_cable post_.” (Y is grounded.) _Both_ battery leads are left connected to the key. The shunt should be on 0. Close the battery switch. Close the testing key to the right. Turn the shunt gradually to the unity post. The galvanometer deflection should be zero. Turn the shunt to 0. Reverse the testing key. Turn the shunt to the unity post. The deflection should be zero. If any deflection is obtained, there is a ground in the battery, the apparatus, or the connections. The test of the cable should not proceed if a deflection is obtained in either position of the key.

In reporting the voltage + to earth and - to earth as “zero” on form, it will be understood that this means zero using the galvanometer, as herein described.

4. _Insulation of leads._—Turn the shunt to 0. Open the battery switch. Connect the earth leads BY and EY to their proper posts. Connect the cable lead, PX, to “cable” post. See that the cable tank ends of the lead PX is disconnected at X and suspended in the air. Close the battery switch. Close the key and turn the shunt to the unity post. Deflections should be as small as possible and in any case _must be steady and uniform for several trials_. Turn the shunt to 0. Reverse the key, stopping at the discharge position. Turn the shunt to the unity post and wait until the galvanometer rests at 0, indicating that the leads are discharged. Turn the shunt to 0. Close the key all the way down. Turn the shunt to the unity post. The deflection should not differ materially from that noted above. If there is a deflection, the trouble is in the lead PX or its connections. Go over these, carefully examining for dust and moisture and noting particularly the proximity of all wires of opposite potential which cross or lie near each other. If there is a small deflection which can not be removed, a correction must be applied subsequently to the deflection obtained in the test for the insulation resistance of the conductor.

Using proper care, there are very few days when perfect insulation of the instruments can not be secured. The lead leakage with well-insulated wire put up properly will be noticed rarely.

5. _Use of Price guard-wire._—As an additional precaution against surface leakage across the insulation at the ends of the conductor it will sometimes be advisable to install an additional lead (not necessarily as carefully insulated as PX) running from the testing switch to the cable under test. This lead should be connected in at the testing switch to the post carrying the lower blade between “D” and “C” (fig. 16); the tank end should be bare of insulation for a sufficient distance to enable the bare wire to be wrapped firmly, without pinching, around the insulation at each end of the particular conductor under test, just below the tapered portion.

The potential difference between the cable core and this guard-wire is thus made practically nil, so that any leakage will be from the guard-wire to the tank, consequently this leakage will not be measured by the galvanometer.

=IV. Take the galvanometer constant as follows=: Open the battery switch.

With a short piece of wire connect the hinge post of the testing key marked “cable” to either “earth” post of the key, the leads to the cable tank being disconnected at E, B, and P. Turn the shunt to 0. Examine the ⅒ megohm box and see that all the resistance coils are in the circuit. Close the battery switch and the testing key. Turn the shunt to the ¹/₁₀₀₀ post. Watch the swing of the galvanometer and when it has come to rest, read and record. Turn the shunt to 0. The galvanometer should return exactly to 0. If it does not, readjust and repeat until it does. The galvanometer constant is numerically equal to the total throw in _smallest_ divisions of the scale multiplied by 100. Remove the connecting wire and replace the leads to the tank.

If at any subsequent time during the test the galvanometer adjustment is disturbed—that is, if it does not return accurately to zero when the shunt is at 0—the constant should be redetermined.

=Testing the cable.=—1. See that the testing key is open and the shunt at 0. Connect the earth lead to ground on the cable armor. Remove the earth connection from No. 1 conductor and connect the cable lead to this conductor; in wet weather the connector joint should be dipped in melted paraffin. (In using paraffin to insulate joints or ends bring it just above 212° F. to evaporate any moisture present. It should not be boiling. The paraffin coating should be at least as thick as the rubber insulation and extend back over the rubber for an inch or more.)

2. Close the testing key to the left (+ to earth), stopping at the discharge position, and turn the shunt to the unity post. There should be no deflection. If there is, it is due either to a charge on the cable, which will disappear after a moment, or to earth currents. (It is assumed that the testing apparatus has been thoroughly tested for insulation.) If due to earth currents, the conductor is probably a poor one. Earth currents are readily recognizable by their fluctuating character. Before assuming that the trouble can not be removed, the joint between the lead and the conductor should be examined again. Moisture on the cable end will give a path for earth currents. Note the value and direction of the throw of the galvanometer and record it.

3. Turn the shunt to 0, close the testing key all the way down (+ to earth), noting the time to the second, or starting the stop watch at the same time, if one is available. The time must be accurately noted. The insulation resistance at the end of one minute’s electrification is the resistance to be reported.

4. When 35 seconds have elapsed, turn the shunt to the ¹/₁₀₀₀-post and watch the galvanometer throw; if small, move the shunt successively to the ¹/₁₀₀-post, to the ¹/₁₀-post, and to the unity post. This operation must be completed before 45 seconds have elapsed from the time the key was closed. With good cable the unity post will always be reached without danger of throwing the galvanometer reading off the scale. Remember that each successive post should give 10 times the throw of the preceding post.

5. At the end of one minute read the deflection, correct for the leakage of the leads and the earth currents, and record. (See example following.)

6. At the end of two minutes read the deflection, correct and record it. For good cable it should be less than the deflection observed at the end of one minute.

7. Turn the shunt to 0, and reverse the key, stopping at the discharge position. Turn the shunt on gradually until the unity post is reached and wait until the reading is 0, indicating that the conductor is discharged. If earth currents are present, 0 will not be reached or will be passed. In this case proceed as before described. A submarine mine cable conductor a mile long will discharge ordinarily in about three minutes.

8. Turn the shunt to 0, stop and start the stop watch; at the same time close the key all the way down (- to earth).

9. After 35 seconds, start turning the shunt, ceasing at 45 seconds. (See paragraph 4, above.)

10. At the end of one minute read the deflection, correct and record it. For good cable it should be substantially the same as the deflection observed at the end of one minute with + of the battery to earth.

11. Turn the shunt to 0, and reverse the key, stopping at the discharge position.

12. Disconnect No. 2 conductor from ground. Disconnect No. 1 from the lead and connect up No. 2. Connect No. 1 to ground. It is not necessary to wait for No. 1 to be discharged completely before disconnecting it.

13. Proceed with No. 2 as with No. 1 and repeat with each conductor.

14. On the completion of the test all conductor ends should be carefully taped.

15. To determine the correct value of the insulation resistance it is essential that the negative pole of the battery be connected to the core of the cable, otherwise the products of electrolysis will tend to seal up any fault which may exist and will cause the conductor to appear better than it really is. With the negative pole of the battery to the core the tendency is to deposit copper on the core and thus to lay bare any fault. The insulation resistance of any conductor is therefore found by multiplying the corrected deflection at the end of one minute, with + of battery to earth, by the denominator of the shunt used, and then dividing the galvanometer constant by this product. The resistance of the ¹/₁₀-megohm box is neglected unless the insulation resistance determined is very low, say, under 1 megohm, when the 100,000 ohms should be subtracted from the above quotient.

16. To determine the insulation resistance per mile at 60° F., multiply the actual insulation resistance found by the length of the cable in miles, and this result by the multiplier furnished by the torpedo depot for the particular make of cable, corresponding to the temperature of the water in the tank observed during test.

_Example._—Leakage of the leads found to be one-half division. Earth currents found to give 1½ divisions in a negative direction from 0 of the scale. Galvanometer throw at the end of one minute (+ to earth), 15 divisions. The corrected deflection is, 15 - ½ + 1½ = 16 divisions.

The galvanometer constant (450 divisions through ¹/₁₀ megohm, shunt at ¹/₁₀₀₀), 45,000 megohms. That is, the battery will give ¹/₁₀ of 450 divisions = 45 through 1 megohm, the shunt at ¹/₁₀₀₀; or, what is the same thing, one division through 45 megohms, the shunt at ¹/₁₀₀₀; therefore with the shunt at unity the battery will give one division through 45 × 1,000 = 45,000 megohms. The insulation resistances = 45,000 ÷ 16 = 2,813 megohms. If the cable is three-fourths mile long, the insulation resistance in megohms per mile is 2,813 × ¾ = 2,110 megohms.

Manufacturer, Safety Insulated Wire & Cable Co.

Temperature of water in tank, 80° F.

Multiplier, 1.7056; 2,110 × 1.7056 = 3,599 megohms insulation resistance per mile at 60° F. This result is recorded on the form.

=VI. Copper resistance.=—1. The drop of potential method is quicker than the bridge method under the usual conditions and should be used if the apparatus is available.

_Apparatus required._—(_a_) Source of power (110 volts D. C. lighting circuit, casemate battery or generator); (_b_) a double-pole single-throw switch to which the power leads are attached; (_c_) a bank of ten 110-volt lamps in parallel; (_d_) a D. C. ammeter of not more than 0-25 scale; (_e_) a D. C. voltmeter, 0-150 scale.

Place the lamp bank and the ammeter in one side of the power line from the switch to the conductor, and the other end of the conductor to the other side of the power line. Connect the voltmeter across the ends of the cable so as to measure the drop of potential between the ends of the conductor being tested. Close the switch, take simultaneous readings on the voltmeter and the ammeter and calculate the resistance. With the apparatus described a conductor 1 mile long will receive about 2½ amperes and show a drop of about 50 volts. The lamps are inserted as a safety precaution. In no case should the current through the conductor exceed 6 amperes. If the cable has been tested for insulation resistance and all the conductors show high insulation, the lamps are not necessary, provided the cable is at least a mile long.

2. The copper resistance found is reduced to that at 60° F. by multiplying by the coefficient found in the following table with the temperature of the water in the tank at the time of the test as an argument:

_Reduction of copper resistance to 60° F._

+--------------+--------++--------------+--------+ | Temperature. | δ || Temperature. | δ | +--------------+--------++--------------+--------+ | _°F._ | || _°F._ | | | 10 | 1.1252 || 55 | 1.0113 | | 11 | 1.1224 || 56 | 1.0090 | | 12 | 1.1196 || 57 | 1.0068 | | 13 | 1.1168 || 58 | 1.0045 | | 14 | 1.1141 || 59 | 1.0023 | | 15 | 1.1113 || 60 | 1.0000 | | 16 | 1.1086 || 61 | .9978 | | 17 | 1.1059 || 62 | .9956 | | 18 | 1.1032 || 63 | .9933 | | 19 | 1.1005 || 64 | .9911 | | 20 | 1.0978 || 65 | .9889 | | 21 | 1.0952 || 66 | .9867 | | 22 | 1.0925 || 67 | .9846 | | 23 | 1.0899 || 68 | .9824 | | 24 | 1.0873 || 69 | .9802 | | 25 | 1.0846 || 70 | .9781 | | 26 | 1.0820 || 71 | .9759 | | 27 | 1.0794 || 72 | .9738 | | 28 | 1.0769 || 73 | .9717 | | 29 | 1.0743 || 74 | .9695 | | 30 | 1.0717 || 75 | .9674 | | 31 | 1.0692 || 76 | .9653 | | 32 | 1.0667 || 77 | .9632 | | 33 | 1.0641 || 78 | .9611 | | 34 | 1.0616 || 79 | .9591 | | 35 | 1.0591 || 80 | .9570 | | 36 | 1.0566 || 81 | .9549 | | 37 | 1.0542 || 82 | .9529 | | 38 | 1.0517 || 83 | .9508 | | 39 | 1.0492 || 84 | .9488 | | 40 | 1.0468 || 85 | .9468 | | 41 | 1.0443 || 86 | .9448 | | 42 | 1.0419 || 87 | .9428 | | 43 | 1.0395 || 88 | .9408 | | 44 | 1.0371 || 89 | .9388 | | 45 | 1.0347 || 90 | .9368 | | 46 | 1.0323 || 91 | .9348 | | 47 | 1.0300 || 92 | .9328 | | 48 | 1.0276 || 93 | .9308 | | 49 | 1.0252 || 94 | .9288 | | 50 | 1.0229 || 95 | .9269 | | 51 | 1.0206 || 96 | .9250 | | 52 | 1.0182 || 97 | .9231 | | 53 | 1.0159 || 98 | .9211 | | 54 | 1.0136 || 99 | .9192 | +--------------+--------++--------------+--------+

The true length of a cable should be that of its center conductor.

From the size of the conductor and its copper resistance the length of the cable may be computed by use of the following wire table:

_Table of resistances of pure copper wire at 60° F._

+---------+---------+-------------+ | Size | Dia. in | Ohms per | | B. & S. | mils. | 1,000 feet. | +---------+---------+-------------+ | 1 | 289 | 0.11999 | | 2 | 258 | .15130 | | 3 | 229 | .19080 | | 4 | 204 | .24058 | | 5 | 182 | .30338 | | 6 | 162 | .38256 | | 7 | 144 | .48245 | | 8 | 128 | .60831 | | 9 | 114 | .76696 | | 10 | 102 | .96740 | | 11 | 91 | 1.21960 | | 12 | 81 | 1.5379 | | 13 | 72 | 1.9393 | | 14 | 64 | 2.4453 | | 15 | 57 | 3.0134 | | 16 | 51 | 3.8880 | | 17 | 45 | 4.9030 | | 18 | 40 | 6.1827 | | 19 | 36 | 7.8024 | | 20 | 32 | 9.8316 | | 21 | 28.5 | 12.397 | | 22 | 25.3 | 15.625 | | 23 | 22.6 | 19.712 | | 24 | 20.1 | 24.857 | | 25 | 17.9 | 31.343 | | 26 | 15.9 | 39.535 | | 27 | 14.2 | 49.839 | | 28 | 12.6 | 62.848 | | 29 | 11.3 | 79.250 | | 30 | 10.0 | 99.932 | +---------+---------+-------------+

The objections to the use of a bridge for measuring copper resistance are the difficulty of eliminating the resistance of the plug contacts and the time required to secure balance. The resistance of the plug contacts may often be as high as 20 ohms, particularly if used at the tank.

If the bridge is used at all, it should be placed in the testing room, and the same leads employed for testing insulation should be used. The resistance of these leads should first be determined by connecting them together and measuring; this resistance is subtracted from each resistance measured.

=VII. General.=—The key to success in cable testing is great care in every detail. The cable now being furnished is all tested with galvanometers having constants from 200,000 to 250,000 megohms. It has all been accepted after most careful test. The chances are that it is good when it arrives at the post, unless it has been mechanically injured in transit, which should be ascertained by careful inspection when delivered at the post.

Do not accept a single measurement if it shows low resistance, but repeat until certain of results. The time between trials on the same conductor should be as great as practicable. For example: Measurements showing low resistance made in the morning should be repeated in the afternoon; those made in the afternoon should be repeated the next day; the conductor being connected to earth during the interval between tests.

APPENDIX NO. 5.

CARE AND PRESERVATION OF SUBMARINE MINE MATÉRIEL.

Frequent inspections of all articles of submarine mine equipment should be made, not only to check up the property, but also to determine the condition of all matériel, and especially to see if it has been affected by dampness. These inspections should be thorough and detailed, as only in this manner can there be impressed on those directly charged with the care of the property the importance of ventilation, dryness, and the proper use of preservatives.

The generating set, storage battery, motor-generators, casemate transformers, power panel, and operating boards will be installed in the mining casemate, and such tools, appliances, and materials as may be used when this apparatus is in commission will also be kept there.

The explosive will be kept in the magazines and tested and cared for in the manner prescribed in Appendix No. 1.

The multiple and single conductor cable will be kept in the cable tanks as described in Appendix No. 4.

All other articles of equipment will ordinarily be kept in the storehouse, and a noncommissioned officer will be placed directly in charge. It shall be his duty to keep the matériel in the best possible condition, using such details from the submarine mine detachment from time to time as may be necessary to assist him in this work. He shall check up all articles taken from the storehouse during practice and report at the end of the day’s work any shortage in tools or appliances that he may discover.

Paints and oils should be kept separate from other stores, and the floor where kept should be covered with 2 or 3 inches of sand, to be renewed occasionally. Sawdust should never be used for this purpose. Cotton waste which has become unfit for use should be promptly burned. Fuses must not be stored with other explosives.

Gasoline in considerable quantities should be stored in tanks underground and never inside of buildings. Small quantities should be kept outside of buildings in some safe place.

When oil engines or generators are out of commission, their bright parts should be covered with light slushing oil. Brass screw threads and parts of tools that are liable to rust should be covered also. In all cases the light slushing oil should be applied in a thin coat, since this is all that is necessary to give good protection. Before applying the light slushing oil to any surface it should be thoroughly cleaned, so as to be free from rust, water, kerosene and lubricating oil, as their presence will cause rusting underneath the slushing oil. The protected surfaces should be occasionally inspected and the coating of slushing oil renewed as often as required.

Screw threads of mine cases, steel screw threads of compound plugs, bolts, nuts and washers, and surfaces of flat joints should be kept coated with the light slushing oil or a mixture of machine oil and graphite.

No oils or grease should ever be placed on points where metallic contact of electrical instruments is necessary, nor on india rubber, ebonite, or slate.

Mine cases should rest on racks or skids, and where space permits should not be in contact with each other. In handling mine cases care must be taken not to damage the bails and bolts. They should be arranged so that the holes in the mine cases can be seen easily; these holes should be fitted with a wooden plug which has been thoroughly greased all over its surface. New mine cases, if galvanized, usually will not need painting until they have been in the water. When taken from the water they should be thoroughly dried, and if they should show signs of rust they should be gone over thoroughly with steel wire brushes until the rust is removed. Parts which can not be reached with the brush should be cleaned with three-cornered steel scrapers. A heavy coat of red lead should then be applied. Seven gallons of this paint can be made by mixing 100 pounds of red lead ground in oil with 5 gallons of raw linseed oil. This mixture should be applied within two or three weeks after mixing. One gallon of paint should give 10 mine cases one coat. After this coat has been allowed to dry there should be applied a coat of white lead toned down to a neutral gray. Seven gallons of this paint can be made by mixing 100 pounds white lead, 2½ gallons raw linseed oil, 2½ gallons turpentine, 1 gallon liquid drier, and adding about 1 pound of lampblack to tone down the mixture.

Mines treated in this way, if kept in a dry storehouse, and not put in the water, should not require repainting for several years. Frequent inspection should be made, however, for in handling the cases and changing their positions on the racks, it will often happen that an abrasion will be made in the surface of the paint, which if neglected may serve as the starting point of a progressive corrosion, which may extend rapidly under the surface of the paint. Should loose paint or rust be seen the case should be repainted. A small wooden mallet may be used to tap the case at all points to loosen scales of rust or paint; then the surface should be thoroughly wire brushed or scraped and the cases repainted as stated above. The inside of mine cases must be inspected to see that the interior surfaces are kept free from rust.

Ground mines and ground mine buoys should be treated in the manner just described for buoyant mine cases.

If the oil engine has not been painted, it should be given a priming coat of red lead mixed in oil. This should be rubbed down with pumice stone and two coats of steel-colored paint applied. The second coat should be rubbed down and two coats of varnish then applied. After this the engine should not need repainting for a couple of years. When, however, repainting is necessary, the engine should be rubbed down until all the varnish is removed and a coat of steel-colored paint applied. This coat should be rubbed until no brush marks remain, and one or two coats of varnish should then be applied. The steel-colored paint should be applied flat; that is, the color which is ground in Japan should be mixed with turpentine. One gallon of this paint is more than sufficient to give an engine two coats.

The motor-generators and the casemate transformers usually will not need the priming coat of red lead, as they come from the factory painted. When it is necessary to paint them, one coat of the steel-colored paint and one of varnish will usually be found sufficient.

Anchors, distribution boxes, junction boxes, mooring sockets, shackles, sister hooks, and the ironwork of operating boards and power panels should be painted with asphaltum varnish.

Paint brushes when new, and before use, should be wrapped or bridled with strong twine and soaked in water to swell. After use they should be cleaned with turpentine and put away in water to keep them from drying and becoming unpliable.

Large ropes should be stored on skids, allowing a free circulation of air. Small ropes should be hung on wooden pins. Ropes should be uncoiled semiannually in dry seasons and stretched out for several days to dry. Wire rope must be stored in a dry place where it will not rust. Marline-covered wire rope should be stored where there is a fair circulation of air. The date of receipt should be stenciled on each reel. If not used at the end of five years it should be run through a bath of pure distilled tar oil. This may be done by setting up an empty reel 20 feet in front of the full reel and placing a tub of the tar oil midway between them. As the rope comes off the full reel it is passed through the oil and the surplus oil slicked off with a piece of burlap, thus returning the oil to the bath. The freshly oiled reel will continue to drip for several days, and sand should be put on the floor under the reel to take up the excess oil. After use in water the marline-covered rope should be thoroughly dried out and then reoiled as above described.

APPENDIX NO. 6.

INSTRUCTIONS FOR MASTERS OF MINE PLANTERS.

The matter contained in this appendix is primarily for the information of the masters of those vessels which are called into service for mine planting purposes upon the outbreak or threatening of hostilities.

The master shall request to be supplied with a copy of Regulations for Mine Planters, U. S. Army.

To each vessel will be assigned a coast artillery officer, who shall be the commanding officer of the vessel. All orders for the vessel shall be given to and through him. He shall have general charge of its business and be responsible for the proper care and disposition of all stores aboard, leaving to the master of the vessel the full and unquestioned control and authority over all matters for which he is professionally responsible.

Any orders to be given by the commanding officer concerning the vessel or its crew will be given to or through the master, except that when planting mines or operating any of the mining appliances or machinery aboard the vessel, the commanding officer, or an officer designated by him, may give instructions directly to any of the vessel’s officers or to members of the vessel’s crew who have duties directly connected with the mining work.

The duties and responsibilities of the master of a vessel engaged in submarine mine work do not differ materially from those devolving upon him when his vessel is otherwise employed. With respect to every duty the vessel may be called upon to perform, it may be stated that explicit directions as to where the vessel is to go and just what maneuvers it is to execute in the mine field will be given by the officer aboard, and it is then incumbent upon the master to execute the maneuver according to his best judgment.

The duties that vessels employed as mine planters are likely to be called upon to perform are as follows:

1. To lay out the mine fields. 2. To lay the multiple cable. 3. To plant mines. 4. To take up mines (including replacing defective mines by good ones where necessary). 5. To take up the cable.

The commanding officer of the vessel is responsible for the proper equipment of the vessel with the necessary apparatus for mine planting, for the loading of all the matériel prior to the planting, and for the method of procedure under the above heads.

The master of the vessel will carry out the orders of the commanding officer and is concerned only in the handling of his boat to prevent accidents to it and to the boats engaged in the planting.

The following precautions will be observed by masters:

1. If current flows across the mine field the planting vessel, to avoid accidents, should always pass on the downstream side of the yawl boat holding the measuring line.

2. The greatest care should be taken that the measuring line and buoy ropes are not caught in the propellers. If the vessel has twin screws, the upstream propeller should be stopped as soon as the measuring line has been passed to the marking boat. In all cases a man with a boat hook should be posted near the anchor davits and another amidships, to hold the measuring line above the water and clear of the sides of the vessel. Keg buoys, and as much of the buoy rope as possible, should be held on the rail near the stern, letting the rope pay out slowly and under tension, until the propellers are past the rope, then the keg and the remainder of the rope may be thrown overboard.

3. A general rule is never to back either propeller when buoy ropes, measuring lines, or cables are being handled overboard at or near the stern of the vessel.

4. If it becomes absolutely necessary to reverse the propellers when paying out cable, men paying it out must haul it in taut and keep it above the wheel and clear of it. The planting vessel should not pass nearer than 25 feet to the distribution box boat when cable is leading out from the latter, nor should it pass over any cable, if it can be avoided, if the depth is less than 16 feet.

5. The vessel should proceed after passing the distribution box boat on such a course that cable will pay off smoothly without becoming entangled. If a cable becomes fouled and entangled, the end should be “let go” at once at the distribution box boat—the planter should proceed on, not stop nor back its propellers. Mine cable should never be made fast in the distribution box boat until after a mine is dropped. It is much better to drop the mine out of position than to endanger the propellers of the vessel. The propeller nearest the distribution box should be stopped the moment the bow of the vessel passes the distribution box boat on its course to drop a mine.

6. If, in planting, the vessel moves _against_ the direction of the current, there is little danger of overturning the distribution box boat if ordinary caution is observed. Should it be necessary to plant against a cross current or with it, it is best to pass the cable end to the distribution box boat by a launch or small boat. In this way the planter need not pass within 50 or 75 yards of the boat.

7. To avoid getting foul of the buoy rope or mine after the mine is dropped, the helm should be put over so as to throw the stern away from the mine. The vessel should be under good headway so that the propellers may be stopped until they are well past the buoy and buoy ropes of the mine. These points are important; failure to observe them will result disastrously.

In laying multiple cable, the course of the vessel invariably should be against the current. Rather than lay cable with the current it is advisable to postpone laying the cable until a change of the tide causes a favorable direction of current. In the end, time will be saved by waiting. Cable should pay off on the _upstream_ side of the vessel if any cross current is running. All care should be taken that the cable does not get caught in the vessel’s propellers. This is of the greatest importance.

As the cable pays out over a chock near the bow of the vessel a man should stand by with a 3-inch strap in readiness to stop the cable should it be necessary, and two men should manipulate brakes to prevent the cable from paying out too rapidly. This is especially necessary if the water is deeper than 50 feet.

Especial care is necessary in planting mines to avoid: (_a_) Colliding with yawl or distribution box boat; (_b_) picking up cable in the propeller; (_c_) getting the mine cable tangled; (_d_) drifting over the mine after it is dropped.

APPENDIX NO. 7.

MANUAL FOR SMALL BOATS.

The left-hand side of a boat or ship, looking toward the bow, is the _port_ side, and the other is the _starboard_ side. The men who row on the port side are called the _port oars_ and those rowing on the starboard side are called the _starboard oars._

Boats are called single or double banked, according as they have one or two oarsmen to a thwart.

_Thwarts_ are the seats on which the crew sits; the space abaft the after thwart is called the _stern sheet_.

_Floorings_ and _gratings_ are the bottom boards of a boat. They prevent the weight from bearing directly upon the planking.

The _gunwale_ of a boat is the upper rail.

The _yoke_ is an athwartship piece of wood or metal fitting over the rudderhead.

_Yoke lanyards_ are the small lines made fast to the ends of the yoke, by which the rudder is turned and the boat steered.

The _stem_ is the upturned portion of the keel at the bow of the boat, to which the forward ends of the planks are secured.

Oars are said to be double banked when two men pull one oar.

The blade of an oar is the broad flattened part. The handle is the small part of an oar on the inboard end of the loom, which the oarsman grasps when pulling. The loom is the portion of an oar extending from the blade to the handle. The leather is the portion of an oar which rests in the rowlock. This is sometimes covered with canvas, but is usually covered with leather; hence the name.

_Feathering_ is the term applied to the operation of turning the blades nearly flat to the water after the stroke, with the upper edge turned forward, especially valuable in rowing against a head wind.

_Rowlocks_ are forked pieces of metal in which the leather of the oars rests while pulling. Swivel rowlocks are movable, a pin on the rowlock fitting into a socket in the gunwale.

_Thole pins_ are pins set vertically in the gunwale and are used in place of rowlocks.

The _steering rowlock_ is a peculiar form of swivel rowlock (fitted near the stern of a boat) in which the steering oar is shipped. This is sometimes called a crutch.

The _painter_ is a rope secured in the bow for towing or for securing the boat.

_Boat-falls_ are tackles made with two blocks and a length of rope; used for hoisting boats.

The _plug_ is the wooden stopper fitted into a hole in the bottom of a boat to let water in or out.

A _boat breaker_ is a small keg used for carrying fresh water.

A _boat-recall_ is an understood signal made to order a boat’s return.

BOAT ORDERS.

Oars and rowlocks having been placed in the boat, blades of oars toward the bow, rudder and yoke, if any, stepped and the yoke lanyards clear, the men board and take their proper seats. The man pulling the bow-oar is No. 1, the next man is No. 2, and so on, to the man pulling the stern-oar, who is called the “stroke-oar.” The men being seated, with oars handy, the bow-man, who may be No. 1 or an extra man, as convenient, holds onto the wharf, side, or piling, as the case may be, with his boat hook.

_Shove off._—At this command the bow-man shoves the boat clear, giving her headway if possible. He boats his boat hook and takes his seat.

_Up oars._—The crew simultaneously seize and raise their oars smartly to the vertical (guiding on the stroke-oar) and hold them directly in front of them, the blades fore-and-aft, inboard hands grasping the handles, holding the same well down between the knees, outboard hands grasping the looms at the height of the chin.

_Let fall._—The oars are eased down into the rowlocks together, brought level with the gunwale, blades horizontal and all trimmed on the after oars. Oars must not be allowed to splash.

(1) _Give way together_, (2) _GIVE WAY_.

At the first command the men reach well forward, blades nearly vertical, ready for the stroke. At the second command they dip their oars at the same time as the stroke-oar and commence rowing, keeping stroke exactly and all lifting their blades to the height of the gunwale on the return. (Or higher if waves render this necessary.)

TO MAKE A LANDING.

In running alongside a vessel or up to a float-stage or wharf, when several lengths away from same, give the command (while the oars are in the water), _IN BOWS_. The bow oarsman (if there be no extra man in the bow) finishes his stroke, then “tosses” and “boats” his oar, blade to the bow, and stands ready with the boat hook to fend off and hold the landing. When there is sufficient headway to carry the boat properly to the landing, give the command, _WAY ENOUGH_. This order is given while the oars are in the water; the men finish the stroke, then toss and boat their oars with as little noise as possible. The oars are next the rail, the after oars outboard of the bow oars. If the stroke oarsman is provided with a boat hook, he grasps it and stands ready to help the bow man.

If it be desired to stop rowing temporarily, give the preparatory command, (1) _Stand by to lay on oars_, at which the crew pays strict attention. Then, when ready, give (2) _OARS_. At this command, given while the oars are in the water, the crew finishes the stroke and brings the oars level with the gunwale, blades horizontal, trimmed on the after oars. This position is also used for salutes, as noted hereafter.

If about to pass so close to another boat that a collision of oars seems probable, command (1) _Trail_, (2) _OARS_. At the second command, given while the oars are in the water, the men finish the stroke, and then, while the oars are still in the water, by lifting the handles with their outboard hands the looms are thrown out of the rowlocks. The men carry their hands outboard till the backs of their wrists rest on the rails and the oars trail astern. (This movement is used in shooting bridges, where lack of head room precludes _tossing_.)

To bring the oars inboard, command: _OARS_.

At this command the men raise the handles, =lower= the looms into the rowlocks, and then raise the blades out of the water and swing the oars to the regular position of _Let fall_.

In order to turn the boat short around (being stationary or nearly so) command: (1) _Give way, starboard_; _back port_, (2) _GIVE WAY_; or (1) _Give way, port_; _back_, _starboard_, (2) _GIVE WAY_. The crew keeps stroke just as regularly as in pulling straight away. As soon as the boat points in the desired direction command: (1) _Give way together_, (2) _GIVE WAY_.

If it be desired to check the boat’s headway, command: _HOLD WATER_. At this command the men drop their blades vertically into the water, tops of blades inclined slightly forward, inboard hands grasping the handles, outboard arms over the looms to steady the oars against the chest. To prepare the crew for rowing command _OARS_, at which they resume the position described under the heading _Let fall_.

To move the boat astern command _STERN ALL_.

At this command the men back water, keeping stroke as regularly as in ordinary rowing. To resume the position of attention give the command _OARS_, as before.

To toss oars command: (1) _Stand by to toss_, (2) _TOSS_.

The command of execution is given while the oars are in the water, the stroke is completed and the oars raised smartly to the vertical, with blades in fore-and-aft plane, handles of oars on bottom boards, the wrists of the inboard hands resting on the thighs, outboard hands grasping the looms at the height of the chin, crew sitting upright. To place the oars in the boat give the command _BOAT YOUR OARS_. At this command the oars are lowered toward the bow (not swung outboard) and laid in the boat as before described. This command may be given from the position of _Let fall_, in which case the men toss their oars and proceed as above.

NOTES.

In rowing the blade of the oar should be raised as high as the gunwale after leaving the water and feathered by dropping the wrist. A barely perceptible pause should be made, and the oar next thrown well forward and dropped edgewise into the water, taking care to avoid splashing and chopping. Now swing the oar smartly through the water without giving it any final jerk, and repeat as above. With green crews it may be found necessary for the coxswain to call _stroke, stroke_, in order to get the men to pull exactly together.

There should be a mark on the loom of the oar (about the height of the eyes when the oar is at _toss_) to show when the blade is fore-and-aft, thus avoiding the necessity of the men gazing up for the purpose of finding out when this is the case. Never allow a boat’s crew to splash with the blades when executing _Let fall_. When resting on oars, insist that they be kept level with the gunwale and at right angles to the keel. Talking among the crew and turning the heads to look at any object should never be allowed while the boat is under way. In most cases, boats should be permanently equipped with a small breaker of fresh water, a spare oar and oarlock and a suitable anchor or grapnel. The anchor rope to withstand a storm should be six (6) times as long as the greatest depth liable to be used as an anchorage. For any small boat in our service a 20-pound anchor and 12-thread (about 1 inch) manila hawser should easily weather a hurricane. A boat should never go out at night without a good, well-filled lantern. Many a boat has been run down through its inability to make its presence known. Before leaving the shore in foggy weather, provide the boat with some sort of a foghorn and a compass, and calculate as nearly as possible the bearings of the landing you wish to make. Take the opposite of this upon returning, making due allowance for tide and wind in both cases. To ride out a gale of wind in an open boat, lash the oars and grating together, making them into a bulky bundle and weight them if possible; span them with the painter and pitch them overboard. This will keep the boat’s head to the sea and prevent her from drifting fast. Assist the boat to take the seas head-on by means of a steering oar. In rowing through a chop, where the rudder is apt to be pitched clear of the water, it should be unshipped and a steering oar used instead. Remember, in making a landing, that the heavier the boat is laden the longer she will keep her way. If you are being towed by a steamer, make her give you a line, instead of using your own, and belay it so it can be cast off in a hurry. Carefully avoid weighing down the bow; always use a short towline when the boat is empty and a long towline when the boat is laden. If the boat’s painter is used for a towline, have a knife ready for cutting it if it becomes necessary. Never go close under a steamer’s stern unless it is absolutely unavoidable.

Officers in boarding a ship, use the starboard gangway, although they may use the port gangway. Enlisted men use the port gangway or the booms, unless otherwise ordered.

_Boat salutes._—The following salutes should be exchanged between boats meeting or passing each other. No junior should pass ahead of a senior without permission.

The junior should always salute first, and the senior should return the salute by touching his cap.

Salutes should be exchanged whenever boats pass near enough to each other for the senior officer to be recognized, whether he be in uniform or not.

Officers without a flag or pennant flying should be saluted with the hand only; those with a flag or pennant flying should, in addition, be saluted by laying on oars.

When a noncommissioned officer is in a boat and meets another boat containing an officer he stands and salutes. If the boat flies a flag or pennant, the noncommissioned officer, in addition, lays on oars.

Officers of the Navy and Marine Corps and foreign officers in boats should always be saluted when recognized.

In laden boats, towing boats, or boats under sail the hand salute only is made on all occasions.

Coxswains in charge of boats shall always rise and salute when officers enter or leave their boats.

Boat keepers shall stand up and salute officers passing in boats and remain standing until the boat has come alongside or passed.

APPENDIX NO. 8.

SUPPLY LIST.

APPARATUS.

Ammeters, portable, 0-25 scale, 1 to each post. Anchors, buoy, 500 pounds, 5 to each group of 19 mines. Anchors, mine, 1 to each buoyant mine. Axle, cable-reel, 1 to each cable-reel frame. Balances and weights, 1 set to each post. Battery, storage, 1 to each casemate. Boards, operating, 1 to each group of 19 mines. Boxes, distribution, 1 to each group of 19 mines. Boxes, distribution, 1 to each group of 7 mines. Boxes, junction, large, 3 to each mile of multiple cable. Boxes, junction, small, 1 to each mile of single-conductor cable. Buoy, distribution box, 1 to each distribution box. Buoy, marking, 5 to each group of 19 mines. Buoy, mine, 1 to each buoyant mine. Cable, submarine, 19-conductor, according to project. Cable, submarine, 7-conductor, according to project. Cable, submarine, 1 conductor, according to project. Cases, guncotton, as required. Circuit closer, 1 to each mine transformer. Clips, cable, 2 for each mine. Engine, internal combustion, 1 to each casemate. Frame, cable-reel, 3 to each post. Fuse can, 1 to each compound plug. Generator, casemate, 1 to each casemate. Mine cases, according to project. Motor generator, D. C.-A. C., 2 to each casemate. Panels, power, 1 to each casemate. Planting equipment for emergency vessels, 1 to each vessel: Each planting equipment consists of— 1 axle, cable-reel. 4 blocks, snatch. 4 blocks, triplex, 2-ton. 2 come-alongs. 2 davits, anchor. 2 davits, mine. 1 frame, cable-reel. 4 hooks, trip. Plugs, compound, 1 to each mine case. Reels, cable, according to cable on hand. Reel and frame, measuring, 1 to each mine field. Shackles, anchor, 2 to each anchor. Shackles, mine, 2 to each mine. Sister hooks, 1 pair to each anchor. Sockets, mooring, 2 to each buoyant mine, for wire rope only. Springs, automatic anchor, 6 extra for each group of 19 mines. Switches, starting, 1 to each motor generator, D. C.-A. C. Telephones, boat, 4 to each mine field. Testing set, insulation, 1 to each post having a cable tank: Each testing set consists of— 1 box, resistance, 100,000 ohms. 2 cases for instruments. 1 galvanometer, D’Arsonval, reflecting. 1 key, special insulation testing. 1 repair kit. 1 shunt, Ayrton Universal. Transformer, casemate, 2 to each casemate. Transformer, mine, 1 to each mine. Voltmeter, portable, 0-3-volt scale, 1 to each storage battery. Voltmeter, portable, 0-150-volt scale, 2 to each post. Weights, distance, for automatic anchor, 6 extra for each group of 19 mines.

UTENSILS.

(Supply for each post, unless otherwise indicated.)

1 anvil, 50-pound. 3 axes, handled. 6 basins, wash. 24 binding posts (to each casemate). 2 blocks, tackle, double. 2 blocks, tackle, single. 6 boxes, tool. 6 brushes, battery. 6 brushes, dust. 6 brushes, paint, flat. 6 brushes, paint, oval. 12 brushes, sash. 12 brushes, scratch. 6 buckets, galvanized iron. 1 chest, carpenter’s tool: The chest contains the following tools— 1 bits, set, of 13. 1 bit, expansive, 1 brace, ratchet. 1 chisels, carpenter’s, set of 6. 1 hammer, claw. 1 knife, drawing. 1 level, carpenter’s. 1 oilstone. 1 plane, jack. 1 plane, smooth. 1 rule, 2-foot. 1 saw, compass. 1 saw, hand. 1 saw, rip. 1 saw set. 1 square, carpenter’s. 6 chisels, cold. 4 clips, wire rope (for each buoyant mine). 4 coppers, soldering. 3 crowbars. 6 cups, drinking. 2 cutters, cable. 1 dies, letters, set. 1 dies, numbers, set. 1 drill, breast. 1 drill points, set of 15. 6 files, 6-inch, flat bastard. 3 files, 6-inch, slim taper. 6 funnels, loading, large. 6 funnels, loading, small. 1 gloves, rubber, pair (to each storage battery). 1 grindstone. 24 hacksaw blades. 4 hacksaw frames. 6 hammers, ball peen. 6 hammers, smith’s. 2 handles, with tools. 3 hatchets. 6 hooks, boat. 2 hydrometers, battery (to each storage battery). 3 irons, calking. 4 irons, grappling. 120 knives, submarine mine (for each mine company, to be issued as part of equipment). 3 ladles. 6 lamps, alcohol. 2 lamps, battery inspection (to each storage battery). 3 lamps, Khotal. 5 leads, sounding. 12 levers for socket wrenches. 12 life buoys. 12 life preservers. 2 mallets, large. 2 mallets, small. 12 marlinespikes. 6 megaphones. 1 oilers and tray, set (to each casemate). 12 padlocks, brass, with chain. 2 pitchers, acid (to each storage battery). 2 plates, earth. 70 pliers, side cutting, 5½ inch (for each mine company, to be issued as part of equipment). 50 pliers, side cutting, 8-inch (for each mine company, to be issued as part of equipment). 3 pots, melting. 4 pumps, boat (to each mine field). 2 scales, extension spring, reading 200 pounds. 1 scales, portable platform. 6 scissors, 8-inch. 6 scoops, large, for trotol only. 6 scoops, small, for trotol only. 12 scrapers, iron, with handle. 4 screw-drivers, large. 4 screw-drivers, medium. 4 screw-drivers, small. 6 switches, assorted (to each casemate). 2 syringes, battery (to each storage battery). 3 tapes, measuring. 2 thermometers, battery (to each storage battery). 2 thermometers, cable tank. 2 thimbles, galvanized iron (to each buoyant mine case). 2 tongs, cable-reel. 6 torches, gasoline, hand. 2 trucks, mine case. 6 vises, bench, large. 6 wrenches, monkey, 8-inch. 6 wrenches, monkey, 15-inch. 12 wrenches, =S=. 6 wrenches, socket. 6 wrenches, spanner. 3 wrenches, Stillson. 6 wrenches, =T=, small.

EXPENDABLE STORES.

Alcohol, wood, 5 gallons to each post. Antimony for socket alloy, 10 pounds to each 19 mines. Books, record of cable test, 1 to each post. Books, daily test, 2 to each post. Books, note, 24 to each post. Brushes, carbon, 4 extra for each machine requiring them. Brushes, wire, 4 extra for each machine requiring them. Cells, dry, large, 25 to each post. Cells, dry, small, 100 to each post. Cement, rubber, 3 pounds to each 19 mines. Cleats, porcelain, 1-wire, 50 to each casemate. Cleats, porcelain, 2-wire, 50 to each casemate. Collars, Turk’s-head, large, 10 to each mile of 7-conductor cable. Collars, Turk’s-head, medium, 10 to each mile of 19-conductor cable. Collars, Turk’s-head, small, 5 to each mine. Compound, commutator, 1 stick to each casemate. Connectors, double, 25 to each casemate. Cords, telephone, 4 extra. Crayons, marking, 12 to each storehouse. Cut-outs, porcelain, 2 to each casemate. Drier, as required. Electrolyte, specific gravity 1210, 4 carboys to each casemate. Explosive, according to project. Fuses, service, 4 to each mine. Gasoline, for torches, 10 gallons to each post. Glands for compound plugs, 2 extra for each plug. Glue, 5 pounds to each post. Graphite, as required. Handles, assorted, as required for repairing tools. Insulators, glass, 25 to each storehouse. Jointers, copper, 1 pound to each 19 mines. Keys, distribution box, flat, 4 extra to each box. Keys, distribution box, split, 4 extra to each box. Keys, mine case, 2 extra for each mine case. Keys, shackle, 1 extra to each shackle. Knobs, porcelain, 100 to each post. Lampblack, 2 pounds to each 100 pounds of white lead. Lamps, incandescent, white, 110 volts, 16-candlepower, 12 to each casemate. Lamps, incandescent, white, 80 volts, 16-candlepower, 12 to each casemate. Lamps, incandescent, red, 80 volts, 8-candlepower, 3 to each operating board. Lamps, incandescent, green, 45 volts, 8-candlepower, 3 to each operating board. Lamps, incandescent, green, 45 volts, 16-candlepower, 3 to each operating board. Lamps, incandescent, green, 45 volts, 32-candlepower, 3 to each operatingboard. Lead, for socket alloy, 90 pounds for each 19 mines. Lead, red, as required. Lead, white, as required. Line, cod, 2,000 feet to each post. Line, measuring, 2,000 feet to each post. Line, sounding, 500 feet to each post. Lye, as required. Marline, 1 pound to each mine. Nails, assorted sizes, 25 pounds to each post. Needles, cleaning, for Khotal lamps, 6 to each post. Nipples, soft rubber, 1 to each hard rubber fuse can. Oakum, 50 pounds to each post. Oil, cylinder, 5 gallons to each casemate. Oil, dynamo, 1 gallon to each casemate. Oil, lubricating, 1 gallon to each storehouse. Oil, linseed, as required, 3 gallons to 100 pounds of lead. Oil, slushing, 5 gallons to each post. Oil, tar, as required for marline-covered rope. Oil, transformer, 1 gallon to each casemate transformer. Packing, asbestos sheet, 2 pounds to each casemate. Packing, asbestos wick, 1 pound to each casemate. Packings, rubber, 100 to each 19 mines. Paint, acid-resisting, as required. Paint, steel color, for casemate apparatus, as required. Paste, soldering, 1 pound to each post. Paraffin, 10 pounds to each post. Pencils, lead, 6 dozen to each post. Plugs, attachment, 6 to each post. Pomade, Putz, 3 pounds to each post. Primers, explosive, 1 to each mine charge. Pumice stone, 2 pounds to each casemate. Resin, 2 pounds to each post. Rope, for distance weight, 20 feet for each automatic anchor. Rope for heaving lines, 1,200 feet to each post. Rope for lashings, 1,200 feet to each post. Rope, marline-covered, according to project. Rope, raising, 50 per cent more than of mooring rope. Rope, wire mooring, according to project. Rosettes, 24 to each post. Ruberine, 5 gallons to each post. Sandpaper, 48 sheets to each post. Sapolio, 10 cakes to each post. Screws, brass, assorted sizes, 1 gross when required. Screws, iron, assorted sizes, 1 gross when required. Screws, set, for compound plugs, 1 extra set for each compound plug. Screws, set, for mine transformers, 1 extra set for each mine transformer. Shellac for insulation purposes, 5 pounds to each post. Soap, 25 cakes to each post. Sockets, lamp, 12 to each casemate. Solder, wire, 5 pounds to each post. Staples, large, 20 pounds to each post. Staples, small, 1 pound to each post. Suspensions, galvanometer, lower, 3 to each insulation testing set. Suspensions, galvanometer, upper, 6 to each insulation testing set. Tags, brass, 50 per group of 19 mines. Tags, lead, 50 per group of 19 mines. Tags, linen, 50 per group of 19 mines. Tape, protective, 5 pounds to each 19 mines. Tape, rubber, 5 pounds to each 19 mines. Tinfoil, 1 pound to each 19 mines. Towelling, 10 yards to each post. Tubes, porcelain, 12 to each post. Turpentine, as required. Twine, 3 pounds to each 19 mines. Varnish, asphaltum, as required. Varnish, spar, as required. Washers, brass, 100 to each 19 mines. Washers, lead, 1 extra set for each compound plug. Waste, cotton, 50 pounds to each post. Wire, casemate, extra, 100 feet each of black, blue, red, and brown to each casemate. Wire, fuse, 1 pound each of 3, 12, and 25 ampere to each casemate. Wire, lamp-cord, extra 100 feet to each casemate. Wire, loading, 20 feet to each mine. Wire, soft-drawn copper.

_Remarks_:

(_a_) Clips and thimbles, scales, extension spring, marline-covered rope, and parts for automatic anchors are required only at posts supplied with automatic anchors.

(_b_) Loading scoops are required only at posts supplied with trotol.

(_c_) In the case of articles to be supplied “as required” it is not contemplated that they shall be kept on hand in larger quantities than required for immediate needs.

[Illustration: FIG. 17a.—IMPROVISED MINE TARGET.]

[Illustration: FIG. 17b.—IMPROVISED MINE TARGET.]