Part 3

The method adopted for dividing up the fundamental interval of any thermometer into sections and steps for calibration may be widely varied, and is necessarily modified in cases where auxiliary bulbs or "ampoules" are employed. The Paris mercury-standards, which read continuously from 0° to 100° C., without intermediate ampoules, were calibrated by Chappuis in five sections of 20° each, to determine the corrections at the points 20°, 40°, 60°, 80°, which may be called the "principal points" of the calibration, in terms of the fundamental interval. Each section of 20° was subsequently calibrated in steps of 2°, the corrections being at first referred, as in the example already given, to the mean degree of the section itself, and being afterwards expressed, by a simple transformation, in terms of the fundamental interval, by means of the corrections already found for the ends of the section. Supposing, for instance, that the corrections at the points 0° and 10° of Table III. are not zero, but C° and C' respectively, the correction C_n at any intermediate point n will evidently be given by the formula,

C_n = C° + c_n + (C' - C°)n/10 (3)

where c_n is the correction already given in the table.

If the corrections are required to the thousandth of a degree, it is necessary to tabulate the results of the calibration at much more frequent intervals than 2°, since the correction, even of a good thermometer, may change by as much as 20 or 30 thousandths in 2°. To save the labour and difficulty of calibrating with shorter threads, the corrections at intermediate points are usually calculated by a formula of interpolation. This leaves much to be desired, as the section of a tube often changes very suddenly and capriciously. It is probable that the graphic method gives equally good results with less labour.

_Slide-Wire._--The calibration of an electrical slide-wire into parts of equal resistance is precisely analogous to that of a capillary tube into parts of equal volume. The Carey Foster method, employing short steps of equal resistance, effected by transferring a suitable small resistance from one side of the slide-wire to the other, is exactly analogous to the Gay Lussac method, and suffers from the same defect of the accumulation of small errors unless steps of several different lengths are used. The calibration of a slide-wire, however, is much less troublesome than that of a thermometer tube for several reasons. It is easy to obtain a wire uniform to one part in 500 or even less, and the section is not liable to capricious variations. In all work of precision the slide-wire is supplemented by auxiliary resistances by which the scale may be indefinitely extended. In accurate electrical thermometry, for example, the slide-wire itself would correspond to only 1°, or less, of the whole scale, which is less than a single step in the calibration of a mercury thermometer, so that an accuracy of a thousandth of a degree can generally be obtained without any calibration of the slide-wire. In the rare cases in which it is necessary to employ a long slide-wire, such as the cylinder potentiometer of Latimer Clark, the calibration is best effected by comparison with a standard, such as a Thomson-Varley slide-box.

_Graphic Representation of Results._--The results of a calibration are often best represented by means of a correction curve, such as that illustrated in the diagram, which is plotted to represent the corrections found in Table III. The abscissa of such a curve is the reading of the instrument to be corrected. The ordinate is the correction to be added to the observed reading to reduce to a uniform scale. The corrections are plotted in the figure in terms of the whole section, taking the correction to be zero at the beginning and end. As a matter of fact the corrections at these points in terms of the fundamental interval were found to be -29 and -9 thousandths respectively. The correction curve is transformed to give corrections in terms of the fundamental interval by ruling a straight line joining the points +29 and +9 respectively, and reckoning the ordinates from this line instead of from the base-line. Or the curve may be replotted with the new ordinates thus obtained. In drawing the curve from the corrections obtained at the points of calibration, the exact form of the curve is to some extent a matter of taste, but the curve should generally be drawn as smoothly as possible on the assumption that the changes are gradual and continuous.

The ruling of the straight line across the curve to express the corrections in terms of the fundamental interval, corresponds to the first part of the process of calibration mentioned above under the term "Standardization." It effects the reduction of the readings to a common standard, and may be neglected if relative values only are required. A precisely analogous correction occurs in the case of electrical instruments. A potentiometer, for instance, if correctly graduated or calibrated in parts of equal resistance, will give correct relative values of any differences of potential within its range if connected to a constant cell to supply the steady current through the slide-wire. But to determine at any time the actual value of its readings in volts, it is necessary to standardize it, or determine its scale-value or reduction-factor, by comparison with a standard cell.

[Illustration: CALIBRATION CURVE.]

A very neat use of the calibration curve has been made by Professor W.A. Rogers in the automatic correction of screws of dividing machines or lathes. It is possible by the process of grinding, as applied by Rowland, to make a screw which is practically perfect in point of uniformity, but even in this case errors may be introduced by the method of mounting. In the production of divided scales, and more

## particularly in the case of optical gratings, it is most important

that the errors should be as small as possible, and should be automatically corrected during the process of ruling. With this object a scale is ruled on the machine, and the errors of the uncorrected screw are determined by calibrating the scale. A metal template may then be cut out in the form of the calibration-correction curve on a suitable scale. A lever projecting from the nut which feeds the carriage or the slide-rest is made to follow the contour of the template, and to apply the appropriate correction at each point of the travel, by turning the nut through a small angle on the screw. A small periodic error of the screw, recurring regularly at each revolution, may be similarly corrected by means of a suitable cam or eccentric revolving with the screw and actuating the template. This kind of error is important in optical gratings, but is difficult to determine and correct.

_Calibration by Comparison with a Standard._--The commonest and most generally useful process of calibration is the direct comparison of the instrument with a standard over the whole range of its scale. It is necessary that the standard itself should have been already calibrated, or else that the law of its indications should be known. A continuous current ammeter, for instance, can be calibrated, so far as the relative values of its readings are concerned, by comparison with a tangent galvanometer, since it is known that the current in this instrument is proportional to the tangent of the angle of deflection. Similarly an alternating current ammeter can be calibrated by comparison with an electrodynamometer, the reading of which varies as the square of the current. But in either case it is neccessary, in order to obtain the readings in amperes, to standardize the instrument for some particular value of the current by comparison with a voltameter, or in some equivalent manner. Whenever possible, ammeters and voltmeters are calibrated by comparison of their readings with those of a potentiometer, the calibration of which can be reduced to the comparison and adjustment of resistances, which is the most accurate of electrical measurements. The commoner kinds of mercury thermometers are generally calibrated and graduated by comparison with a standard. In many cases this is the most convenient or even the only possible method. A mercury thermometer of limited scale reading between 250° and 400° C., with gas under high pressure to prevent the separation of the mercury column, cannot be calibrated on itself, or by comparison with a mercury standard possessing a fundamental interval, on account of difficulties of stem exposure and scale. The only practical method is to compare its readings every few degrees with those of a platinum thermometer under the conditions for which it is to be used. This method has the advantage of combining all the corrections for fundamental interval, &c., with the calibration correction in a single curve, except the correction for variation of zero which must be tested occasionally at some point of the scale.

AUTHORITIES.--Mercurial Thermometers: Guillaume, _Thermométrie de Précision_ (Paris, 1889), gives several examples and references to original memoirs. The best examples of comparison and testing of standards are generally to be found in publications of Standards Offices, such as those of the Bureau International des Poids et Mésures at Paris. Dial Resistance-Box: Griffiths, _Phil. Trans._ A, 1893; Platinum Thermometry-Box: J.A. Harker and P. Chappuis, _Phil. Trans._ A, 1900; Thomson-Varley Potentiometer and Binary Scale Box: Callendar and Barnes, _Phil. Trans._ A, 1901. (H. L. C.)

CALICO, a general name given to plain cotton cloth. The word was spelt in various forms, including "calicut," which shows its derivation from the Indian city of Calicut or Kolikod, a seaport in the presidency of Madras, and one of the chief ports of intercourse with Europe in the 16th century, where cotton cloths were made. The name seems to have been applied to all kinds of cotton cloths imported from the East. In England it is now applied particularly to grey or bleached cotton cloth used for domestic purposes, and, generally, to any fairly heavy cotton cloth without a pattern. In the United States there is a special application to printed cloth "of a coarser quality than muslin." In England "printed calico" is a comprehensive term.

CALICUT, a city of British India, in the Malabar district of Madras; on the coast, 6 m. N. of Beypur. In 1901 the population was 76,981, showing an increase of 14% in the decade. The weaving of cotton, for which the place was at one time so famous that its name became identified with its _calico_, is no longer of any importance. Calicut is of considerable antiquity; and about the 7th century it had its population largely increased by the immigration of the Moplahs, a fanatical race of Mahommedans from Arabia, who entered enthusiastically into commercial life. The Portuguese traveller Pero de Covilham (q.v.) visited Calicut in 1487 and described its possibilities for European trade; and in May 1498 Vasco da Gama, the first European navigator to reach India, arrived at Calicut. At that time it was a very flourishing city, and contained several stately buildings, among which was especially mentioned a Brahminical temple, not inferior to the largest monastery in Portugal. Vasco da Gama tried to establish a factory, but he met with persistent hostility from the local chief (_zamorin_), and a similar attempt made by Cabral two years later ended in the destruction of the factory by the Moplahs. In revenge the Portuguese bombarded the town, but no further attempt was made for some years to establish a trading settlement there. In 1509 the marshal Don Fernando Coutinho made an unsuccessful attack on the city; and in the following year it was again assailed by Albuquerque with 3000 troops. On this occasion the palace was plundered and the town burnt; but the Portuguese were finally repulsed, and fled to their ships after heavy loss. In the following year they concluded a peace with the zamorin and were allowed to build a fortified factory on the north bank of the Kallayi river, which was however again, and finally, abandoned in 1525. In 1615 the town was visited by an English expedition under Captain Keeling, who concluded a treaty with the zamorin; but it was not until 1664 that an English trading settlement was established by the East India Company. The French settlement, which still exists, was founded in 1698. The town was taken in 1765 by Hyder Ali, who expelled all the merchants and factors, and destroyed the cocoa-nut trees, sandal-wood and pepper vines, that the country reduced to ruin might present no temptation to the cupidity of Europeans. In 1782 the troops of Hyder were driven from Calicut by the British; but in 1788 it was taken and destroyed by his son Tippoo, who carried off the inhabitants to Beypur and treated them with great cruelty. In the latter part of 1790 the country was occupied by the British; and under the treaty concluded in 1792, whereby Tippoo was deprived of half his dominions, Calicut fell to the British. After this event the inhabitants returned and rebuilt the town, which in 1800 consisted of 5000 houses.

As the administrative headquarters of the district, Calicut maintains its historical importance. It is served by the Madras railway, and is the chief seaport on the Malabar coast, and the principal exports are coffee, timber and coco-nut products. There are factories for coffee-cleaning, employing several hundred hands; for coir-pressing and timber-cutting. The town has a cotton-mill, a saw-mill, and tile, coffee and oil works. A detachment of European troops is generally stationed here to overawe the fanatical Moplahs.

CALIFORNIA, one of the Pacific Coast states of the United States of America, physically one of the most remarkable, economically one of the more independent, and in history and social life one of the most interesting of the Union. It is bounded N. by Oregon, E. by Nevada and Arizona, from which last it is separated by the Colorado river, and S. by the Mexican province of Lower California. The length of its medial line N. and S. is about 780 m., its breadth varies from 150 to 350 m., and its total area is 158,207 sq. m., of which 2205 are water surface. In size it ranks second among the states of the Union. The coast is bold and rugged and with very few good harbours; San Diego and San Francisco bays being exceptions. The coast line is more than 1000 m. long. There are eight coast islands, all of inconsiderable size, and none of them as yet in any way important.

_Physiography._--The physiography of the state is simple; its main features are few and bold: a mountain fringe along the ocean, another mountain system along the east border, between them--closed in at both ends by their junction--a splendid valley of imperial extent, and outside all this a great area of barren, arid lands, belonging partly to the Great Basin and partly to the Open Basin region.

Along the Pacific, and some 20-40 m. in width, runs the mass of the Coast Range, made up of numerous indistinct chains--most of which have localized individual names--that are broken down into innumerable ridges and spurs, and small valleys drained by short streams of rapid fall. The range is cut by numerous fault lines, some of which betray evidence of recent activity; it is probable that movements along these faults cause the earthquake tremors to which the region is subject, all of which seem to be tectonic. The altitudes of the Coast Range vary from about 2000 to 8000 ft.; in the neighbourhood of San Francisco Bay the culminating peaks are about 4000 ft. in height (Mount Diablo, 3856 ft.; Mount St Helena, 4343 ft.), and to the north and south the elevation of the ranges increases. In the east part of the state is the magnificent Sierra Nevada, a great block of the earth's crust, faulted along its eastern side and tilted up so as to have a gentle back slope to the west and a steep fault escarpment facing east, the finest mountain system of the United States. The Sierra proper, from Lassen's Peak to Tehachapi Pass in Kern county, is about 430 m. long (from Mt. Shasta in Siskiyou county to Mt. San Jacinto in Riverside county, more than 600 m.). It narrows to the north and the altitude declines in the same direction. Far higher and grander than the Coast Range, the Sierra is much less complicated, being indeed essentially one chain of great simplicity of structure. It is only here and there that a double line of principal summits exists. The slope is everywhere long and gradual on the west, averaging about 200 ft. to the mile. Precipitous gorges or canyons often from 2000 to 5000 ft. in depth become a more and more marked feature of the range as one proceeds northward; over great portions of it they average probably not more than 20 m. apart. Where the volcanic formations were spread uniformly over the flanks of the mountains, the contrast between the canyons and the plain-like region of gentle slope in which they have been excavated is especially marked and characteristic. The eastern slope is very precipitous, due to a great fault which drops the rocks of the Great Basin region abruptly downward several thousand feet. Rare passes cross the chain, opening at the foot of the mountains on the east and the west high on their flanks, 7000-10,000 ft. above the sea. Between 36° 20' and 38° the lowest gap of any kind is above 9000 ft., and the average height of those actually used is probably not less than 11,000 ft. The Kearsarge, most used of all, is still higher. Very few in the entire Sierra are passable by vehicles. Some forty peaks are catalogued between 5000 and 8000 ft., and there are eleven above 14,000. The highest portion of the system is between the parallels of 36° 30' and 37° 30'; here the passes are about 12,000 ft. in elevation, and the peaks range from 13,000 ft. upward, Mount Whitney, 14,502 ft., being the highest summit of the United States, excluding Alaska. From this peak northward there is a gradual decline, until at the point where the Central Pacific crosses in lat. 39° 20' the elevation is only 7000 ft.

Of the mountain scenery the granite pinnacles and domes of the highest Sierra opposite Owen's Lake, where there is a drop eastward into the valley of about 10,000 ft. in 10 m.; the snowy volcanic cone of Mt Shasta, rising 10,000 ft. above the adjacent plains; and the lovely valleys of the Coast Range, and the south fork of the King river--all these have their charms; but most beautiful of all is the unique scenery of the Yosemite Valley (q.v.). Much of the ruggedness and beauty of the mountains is due to the erosive action of many alpine glaciers that once existed on the higher summits, and which have left behind their evidences in valleys and amphitheatres with towering walls, polished rock-expanses, glacial lakes and meadows and tumbling waterfalls. Remnants of these glaciers are still to be seen,--as notably on Mt. Shasta,--though shrunk to small dimensions. Glacial action may be studied well as far south as 36°. The canyons are largely the work of rivers, modified by glaciers that ran through them after the rivers had formed them. All of the Sierra lakes and ponds are of glacial origin and there are some thousands of them. The lower lake line is about 8000 ft.; it is lower to the north than to the south, owing to the different climate, and the different period of glacial retrogression. Of these lakes some are fresh, and some--as those of the north-east counties--alkali. The finest of all is Tahoe, 6225 ft. above the sea, lying between the true Sierras and the Basin Ranges, with peaks on several sides rising 4000-5000 ft. above it. It is 1500 ft. deep and its waters are of extraordinary purity (containing only three grains of solid matter to the gallon). Clear Lake, in the Coast Range, is another beautiful sheet of water. It is estimated by John Muir that on an average "perhaps more than a mile" of degradation took place in the last glacial period; but with regard to the whole subject of glacial action in California as in other fields, there is considerable difference of opinion. The same authority counted 65 small residual glaciers between 36° 30' and 39°; two-thirds of them lie between 37° and 38°, on some of the highest peaks in the district of the San Joaquin, Merced, Tuolumne and Owen's rivers. They do not descend, on an average, below 11,000 ft.; the largest of all, on Mt. Shasta, descends to 9500 ft. above the sea.

Volcanic action has likewise left abundant traces, especially in the northern half of the range, whereas the evidences of glacial action are most perfect (though not most abundant) in the south. Lava covers most of the northern half of the range, and there are many craters and ash-cones, some recent and of perfect form. Of these the most remarkable is Mt. Shasta. In Owen's Valley is a fine group of extinct or dormant volcanoes.

Among the other indications of great geological disturbances on the Pacific Coast may also be mentioned the earthquakes to which California like the rest of the coast is liable. From 1850 to 1887 almost 800 were catalogued by Professor E.H. Holden for California, Oregon and Washington. They occur in all seasons, scores of slight tremors being recorded every year by the Weather Bureau; but they are of no importance, and even of these the number affecting any particular locality is small. From 1769 to 1887 there were 10 "destructive" and 24 other "extremely severe" shocks according to the Rossi Forel nomenclatural scale of intensity. In 1812 great destruction was wrought by an earthquake that affected all the southern part of the state; in 1865 the region about San Francisco was violently disturbed; in 1872 the whole Sierra and the state of Nevada were violently shaken; and in 1906 San Francisco (q.v.) was in large part destroyed by a shock that caused great damage elsewhere in the state.

North of 40° N. lat. the Coast Range and Sierra systems unite, forming a country extremely rough. The eastern half of this area is covered chiefly with volcanic plains, very dry and barren, lying between precipitous, although not very lofty, ranges; the western half is magnificently timbered, and toward the coast excessively wet. Between 35° and 36° N. lat. the Sierra at its southern end turns westward toward the coast as the Tehachapi Range. The valley is thus closed to the north and south, and is surrounded by a mountain wall, which is broken down in but a single place, the gap behind the Golden Gate at San Francisco. Through this passes the entire drainage of the interior. The length of the valley is about 450 m., its breadth averages about 40 m. if the lower foothills be included, so that the entire area is about 18,000 sq. m. The drainage basin measured from the water-partings of the enclosing mountains is some three times as great. From the mouth of the Sacramento to Redding, at the northern head of the valley, the rise is 552 ft. in 192 m., and from the mouth of the San Joaquin southward to Kern lake it is 282 ft. in 260 m.