CHAPTER XX
MISCELLANEOUS ELECTRICAL APPARATUS
HOW ELECTRICITY MAY BE GENERATED FROM HEAT
For the past century there has been on the part of many scientists and inventors a constant endeavor to "harness the sunlight." The power which streams down every day to our planet is incalculable. The energy consumed in the sun and thrown off in the form of heat is so great that it makes any earthly thing seem infinitesimal. We can only feel the heat from a large fire a few feet away, yet the scorching summer heat travels 90,000,000 miles before it reaches us, and even then our planet is receiving only the smallest fractional part of the total amount radiated.
Dr. Langley of the Smithsonian Institute estimated that all the coal in the State of Pennsylvania would be used by the sun in a fraction of a second if it were sent up there to supply energy.
Perhaps, some day in the future, electric locomotives will haul their steel cars swiftly from city to city by means of electricity, generated with "sun power." Perhaps energy from the same source will heat our dwellings and furnish us light and power.
This is not an idle dream, but may some day be an actuality. It has already been carried out to some extent. A Massachusetts inventor has succeeded in making a device for generating electricity from sun energy.
The apparatus consists of a large frame, in appearance very much like a window. The glass panes are made of violet glass, behind which are many hundred little metallic plugs. The sun’s heat, imprisoned by the violet glass, acts on the plugs to produce electricity. One of these generators exposed to the sun for ten hours will charge a storage battery and produce enough current to run 30 large tungsten lamps for three days.
[Illustration: Fig. 303.—How the Copper Wires (_C_) and the Silver Wires (_I_) are twisted together in Pairs.]
The principle upon which the apparatus works was discovered by a scientist named Seebeck, in 1822. He succeeded in producing a current of electricity by heating the points of contact between two dissimilar metals.
Any boy can make a similar apparatus, which, while not giving enough current for any practical purpose, will serve as an exceedingly interesting and instructive experiment.
Cut forty or fifty pieces of No. 16 B. & S. gauge German silver wire into five-inch pieces. Cut an equal number of similar pieces of copper wire, and twist each German silver wire firmly together with one of copper so as to form a zig-zag arrangement as in Figure 303.
[Illustration: Fig. 304.—Wooden Ring.]
Next make two wooden rings about four inches in diameter by cutting them out of a pine board. Place the wires on one of the rings in the manner shown in Figure 305. Place the second ring on top and clamp it down by means of two or three screws.
[Illustration: Fig. 305.—Complete Thermopile. An Alcohol Lamp should be lighted and placed so that the Flame heats the Inside Ends of the Wires in the Center of the Wooden Ring.]
The inner junctures of the wires must not touch each other. The outer ends should be bent out straight and be spaced equidistantly. The ring should be supported by three iron rods or legs. The two terminals of the thermopile as the instrument is called, should be connected to binding-posts.
Place a small alcohol lamp or Bunsen burner in the center, so that the flame will play on the inner junctures of the wires. A thermopile of the size and type just described will deliver a considerable amount of electrical energy when the inside terminals are good and hot and the outside terminals fairly good.
The current may be very easily detected by connecting the terminals to a telephone receiver or galvanometer. By making several thermopiles and connecting them in parallel, sufficient current can be obtained to light a small lamp.
HOW TO MAKE A REFLECTOSCOPE
A reflectoscope is a very simple form of a "magic lantern" with which it is possible to show pictures from post-cards, photographs, etc. The ordinary magic lantern requires a transparent lantern slide, but the reflectoscope will make pictures from almost anything. The picture post-cards or the photographs that you have collected during your vacation may be thrown on a screen and magnified to three or four feet in diameter. Illustrations clipped from a magazine or newspaper or an original sketch or painting will likewise show just as well. Everything is projected in its actual colors. If you put your watch in the back of the lantern, with the wheels and works exposed, it will show all the metallic colors and the parts in motion.
[Illustration: Fig. 306.—A Reflectoscope.]
The reflectoscope, shown in Figure 306, consists of a rectangular box nine inches long, six inches wide, and six inches high outside. It may be built of sheet-iron or tin, but is most easily made from wood. Boards three-eighths of an inch thick are heavy enough. The methods of making an ordinary box are too simple to need description. The box or case in this instance, however, must be carefully made and be "light-tight," that is, as explained before, it must not contain any cracks or small holes which will allow light to escape if a lamp is placed inside.
A round hole from two and one-half to three inches in diameter is cut in the center of one of the faces of the box.
The exact diameter cannot be given here because it will be determined by the lens which the experimenter is able to secure for his reflectoscope. Only one lens is required. It must be of the "double-convex" variety, and be from two and one-half to three inches in diameter. A lens is very easily secured from an old bicycle lantern. It should be of clear glass.
[Illustration: Fig. 307.—How the Lens is Arranged and Mounted.]
A tube, six inches long and of the proper diameter to fit tightly around the lens, must be made by rolling up a piece of sheet-tin and soldering the edges together. This tube is the one labeled "movable tube" in the illustrations. A second tube, three inches long and of the proper diameter to just slip over the first tube, must also be made. A flat ring cut from stiff sheet-brass is soldered around the outside of this second tube, so that it may be fastened to the front of the case by three or four small screws in the manner shown. The hole in the front of the box should be only large enough to receive the tube.
The lens is held in position near one end of the movable tube by two strong wire rings. These rings should be made of wire that is heavy and rather springy, so that they will tend to open against the sides of the tube. It is a good plan to solder one of them in position, so that it cannot move, and then put in the lens. After the lens is in position, the second ring should be put in and pushed down against the lens. Do not attempt to put the lens in, however, until you are sure that the metal has cooled again after soldering, or it will be liable to crack.
[Illustration: Fig. 308.—A View of the Reflectoscope from the Rear, showing the Door, etc.]
The back of the box contains a small hinged door about four inches high and five and one-half inches long. The pictures that it is desired to project on the screen are held against this door by two small brass clips, as shown in Figure 308.
[Illustration: Fig. 309.—A View of the Reflectoscope with the Cover removed, showing the Arrangement of the Lamps, etc.]
The light for the reflectoscope is most conveniently made by two 16-candle-power electric incandescent lamps. Figure 309 shows a view of the inside of the box with the cover removed, looking directly down. The lamps fit into ordinary flat-base porcelain receptacles, such as that shown in Figure 310. Two of these receptacles are required, one for each lamp. They cost about ten cents each.
[Illustration: Fig. 310.—A Socket for holding the Lamp.]
The reflectors are made of tin, bent as shown in Figure 311. They are fastened in position behind the lamps by four small tabs.
It is possible to fit a reflectoscope with gas or oil lamp to supply the light, but in that case the box will have to be made much larger, and provided with chimneys to carry off the hot air.
The interior of the reflectoscope must be painted a dead black by using a paint made by mixing lampblack and turpentine. The interior also includes the inside of the tin tubes.
The electric current is led into the lamps with a piece of flexible lamp-cord passing through a small hole in the case. An attachment-plug is fitted to the other end of the cord, so that it may be screwed into any convenient lamp-socket.
[Illustration: Fig. 311.—The Tin Reflector.]
The pictures should be shown in a dark room and projected on a smooth white sheet. They are placed under the spring clips on the little door and the door closed. The movable tube is then slid back and forth until the picture on the screen becomes clear and distinct.
The lantern may be improved considerably by using tungsten lamps of 22 c. p. each in place of ordinary c. p. carbon filament lamps.
If four small feet, one at each corner, are attached to the bottom of the case, its appearance will be much improved.
Very large pictures will tend to appear a little blurred at the corners. This is due to the lens and cannot be easily remedied.
HOW TO REDUCE THE 110-v. CURRENT SO THAT IT MAY BE USED FOR EXPERIMENTING
Oftentimes it is desirable to operate small electrical devices from the 110-v. lighting or power circuits. Alternating current can be reduced to the proper voltage by means of a small step-down transformer, such as that described in