Application of Specific Caloric.--The knowledge of the specific caioric of bodies affords the means of measuring approximately the most elevated temperatures. Thus, if we place in a medium whose temperature is required, a mass of difficultly fusible metal, as a cylinder of platinum. and allow it to remain so long as to acquire the temperature of the medium; then, if we immerse it in water whose weight and temperature are known, and observe the highest temperature which the quid reaches, we can thence deduce from formula (C) the temperature T to which the mass of platinum has been raised, Yet the temperature thus obtained will be only approximate; for we have seen that the specific caloric increases with the temperature, and as we do not know that of the platinum a the elevated temperature to which it has been brought in the supposed experiment, we can only substitute for c in the formula an approximate value.

Latent Caloric of Fusion.-We have seen that when bedies pass from the solid to the liquid state, there is an absorption of a quantity of latent heat; and we proceed to show how to measure the quantity of heat absorbed by the unit of weight. This question is 1esolved by the method of mixtures, on the evident principle that when a body is solidified. it disengages a quantity of heat exactly equal to that which it absorbed Juring fusion. To take an example: suppose it were required to determine the caloric of fusion in lead. We melt a weight of this body, and after having taken from it the temperature , we pour it into a mass of water whose weight m and Lem perature t are known. This being done, et c represent the specific caloric of lead; the caloric of fusion, that is, the quantity of heat absorbed by the unit of weight in melting, or, which is the same thing, that which is restored at the moment of solidification; and the final temperature of the vater heated by the lead. The mass of water being heated from t to 0 degrees, it has absorbed a quantity of heat represented by (0-1); the mass of lead in cooling down from to e, has given out, in one part, a quantity of heat denoted y Me (T-9); and in another, at the moment of solidification, it disengages a quantity of heat represented or wz. eve, therefore, he equation MC (T — 9) + M m (8); - hence, — 81

x=

m (0 − t) — x c (v —0)

We

quantity of heat, which is denominated the caloric of elasticity, or the caloric of vaporisation. In order to determine the quantity of heat absorbed then by the puit of weight of differ ent liquids, we adopt as evident, the principle that a vapour which is liquified, gives on a quantity of caloric precisely equal to that which it had absorbed in vaporisation. The method employed in this case is the same as that resorted to in the determination of the specific calcric of the gases in relation to that of warer. The apparatus employed in this kind of research is exhibited in fig. 223.

The vapour is generated in a retort, c, where its temperature is indicated by a thermometer; it then passes into a worm, es, immersed in cold water. Here it is condensed, and gives out, to the worm and the water in the vessel M, its latent caloric. The water which is produced by the condensation is collected in a vessel, a, and its weight shows the weight of the vapour which has passed through the worn, The thermometers placed in the vessel M, indicate the height to which the temperature of the water has been raised. Now, let devote the weight of the vapour which wes condensed. T its temperature when it entered the worn, and x ita caloric of vaporisation. Also let m be the weight of the water in which the worm is immersed, including that of the vessel and of the wor reduced to water, the initial temperature of the water, and its final temperature. In order to measure the heat giver out by the vapour, we observe that at the commencement of the experiment the water produced by the condensation comes out at the temperature to Cent.; while at the end of it, i ecomes out at 0° Cent.; whence it follows, that during the whole experiment i comes out at a mean temperature between these, that is, at the temperature of (t). The weigh of the vapour has, therefore, given out a quantity of heat denoted by M T(); but at the moment of its Caloris of Melting Ice.-The knowledge of the caloric of the liquefactior, it disengaged a quantity of heat represented by meiting of ice.is interesting on account of its useful appi:ca-M: moreover, the heat absorbed by the cold water, tie tions. It is also determined by the method of mixtures. Thus, worn, and the vessel, is (et). We hare. therefore, the let м denote a mass of ice a: 0 Centigrade, and m a mass of equation мx+ { π- } (¿-|· e) } == ; et,, whence the warm water at 19 Centigrade suflicient to melt all the ice. Let the ice be thrown into the water, and as soon as it is all value of may be found. M. Desprez has ascertained by melted, let the final temperature of the mixture be noted. In this means, for the calorie of elasticity in the vanour of wate 0 represents this temperature, the water being cooled down at 100° Cent., that is, s eam, the number 610; in other words, from to Centigrade to 0. has given out a quantity of heat repre- a gramme of water at 100 Cent, absorba in its "aporisation sented by m (t-0); and if x represents the caloric of the melt- the quantity of hear acessary to raise 540 grammes of water ing of ice, it has absorbed, in order to melt, a quantity of heat fram 0° to 12 Cens.; or, which is the same thing, the quanti denoted by Ma; but it is heated throughout, after the melting, of heat necessary to raise gramme from 0 to 540° Cent. and its temperature rises from 0° to 0° Centigrade; it has there. As 100° Cent are equal to 180° Fahr., we here this proportion fore absorbed a quantity of heat denoted me. We have, there- to express the same quantity in degrees of Fahrenheit's ther fore, the equation MM0m (t0): whence we can mometer, viz., 100: 180: 540 972. herefore 972° Fahr deduce the value of x. By this process, and at the same time expresses what is called the latent heat of steam, according to avoiding with the greatest care all sources of error. MM. La M. Despretz. The latent heat of steam is generally reckone. Provostaye and Desains found that the calcric of the melting in round numbers at 1000° Fabr. of ice is 79, that is, a kilogramme of melted ice absorbs, in the state of latent caloric, the quantity of heat necessary to raise 79 kilogrammes of water from 0 to 1 Centigrade, or which is the same thing, kilogramme of water from 0° to 79° Centi grade.

Latent Caloric of Vaporisation.-We have seen that liquids, when converted into vapour, make latent a very considerable

SOURCES OF HEAT.

The different sources of heat are the following:-1st, the mechanical sources. riz triecon percussion, anu pressure; 2nd, the physical sources, viz. gr adiation, tenerria! hea molecular action, change of state, a ece et y; 3rd, the chemical sources, viz. combination and combustion; 4th, the

physiological sources, viz. the causes of the production of heat in living beings.

Mechanical Sources.-The friction of two bodies against each other develops a quantity of heat which increases with the pressure and velocity with which they are are rubbed. For example, the axle-boxes of carriage wheels, by their friction against the axle, are frequently heated so much as to take fire. Sir H. Davy partly melted two pieces of ice by rubbing them together in an atmosphere below the freezing point. By boring a mass of bronze under water, Count Rumford found that in order to obtain 250 grammes (about half a pound and an ounce) of filings, the heat developed by the friction was sufficient to raise 25 kilogrammes (about 55 pounds) of water from 0° to 100° Cent. In the tinder-box apparatus, it is by the friction of the steel against the flint that the metallic particles, which are detached, are so heated as to take fire in the air. The heat disengaged by friction is attributed to a vibratory motion thus communicated to the particles of bodies. It has been supposed that a cast-iron stove could be made so as to heat the whole of the air of an apartment by the single operation of a motion of rotation. This ingenious process has not only been proposed, but even put in practice in some part of America; but it is evident that this could only be useful where moving power was abundant and of very little value, as in certain mountainous regions, where waterfalls are very considerable, and where, free from the action of frost by their velocity and temperature, they can be found at every step. The following is a representation of a fire-place heated by the friction of a mill-stone, and answering the purpose of cooking victuals and warming the house. See fig. 224.

Fig. 224.

When a body is compressed in such a manner that its density is increased, its temperature rises with the diminution of its volume. This phenomenon, which is scarcely sensible in liquids, is manifested in solids to a considerable degree; and in gases, which are extremely compressible, the disengagement of heat is still greater. The powerful development of heat which is produced by the compression of a gas, is shown in the Tachopyrion, or Fire-syringe. This instrument is composed of a thick glass tube or brass cylinder, in which a piston, covered with leather, moves so as to be air-tight. See fig. 225.

At the bottom of the piston is a small cavity, in which is put

a small piece of amadou or tinder. The tube now being full by the hand; the compressed air then instantly inflames the of air, the piston is quickly and forcibly driven to the bottom amadou, which will be seen burning, if the piston be instantly and rapidly withdrawn from the tube. The inflammation of the tinder in this experiment implies at least a temperature of 300° Cent. or 572° Fahr. At the instant of compression, it produces a very sensible light, which was at first ascribed to the high temperature to which the air has been carried; but it has been discovered to arise from the combustion of the oil with which the piston is greased.

It is by the elevation of temperature which it generates, consequently the detonation of a mixture of oxygen and that pressure is sufficient to produce the combination, and hydrogen. The heat disengaged by compression is explained by the closer bringing together of the particles, which causes a certain portion of latent heat to pass into the state of sensible heat. Percussion is also a source of heat, as may be proved by hammering a malleable metal on an anvil. The heat thus disengaged arises not only from the closer bringing together of the particles, but also from a vibratory motion; for lead, which is not increased in density by percussion, is a metal which does not admit of being thus heated. the most intense is the sun. Physical Sources.-Of all the sources of heat known to us, out by the sun, we are ignorant: some consider it as a flaming Of the cause of the heat given composed of strata which chemically re-act on each other, like mass liable to immense eruptions; while others say that it is the couples in the voltaic pile, and that thus electric currents are generated which are the sources of the solar light and heat. On either hypothesis, the incandescence of the sun would have its limit. Experiments have been made in order to measure the quantity of heat annuelly emitted by the sun. M. Pouillet, by means of an apparatus which he calls the pyrheliometer (sun-fire-measure), has calculated that if the quantity of heat which the earth receives from the sun in the course of a year, were entirely employed in melting ice, it would be capable of melting a stratum of it round the globe of about 34 yards in depth. Now, according to the surface which the earth presents to the radiation of the sun, and according to the distance between them, the earth receives only 2381000000 part of the solar heat.

If we had the sun always at our disposal, however feeble his rays might become at certain times of the year, we could still, by means of very simple artifices, draw from it a sufficient quantity of heat for the purpose of heating our apartments. Thin and transparent bodies, particularly squares of glass, possess with regard to the solar rays a very singular property which cannot be too extensively known. For instance, if we take a box, see fig. 226, having one of its sides open, close

Fig. 225.

Fig. 226.

LESSONS IN PHYSICS.

this opening with a square of glass, and then expose it to the sun, the rays will immediately strike against it. These rays will not all penetrate into the interior of the box, but the greater part of them will pass through the glass and tend to heat the interior. If the opening were not closed by a square of glass, the rays having once reached the interior would go out as freely as they entered, and apart from the influence which they might have on the sides, the temperature of the interior of the box would be the same as that of the exterior. But things happen otherwise in the case of the glass square. The calorific rays have no longer the same facility in going out which they had in going in. The square performs the office If there be only one of a valve which only opens inwardly. square for the rays to pass through, a considerable number of them manage to escape; but if there be a number of squares in succession for the rays to pass through, the more will they be prevented from escaping, and a greater number of rays will remain prisoners. This process will be continually taking place with new rays, and the longer the machine is placed in the sun, the more will they collect, and the more will the heat increase inside. Moreover, the stronger the heat becomes, the greater will be the number of squares necessary to preserve it. But with a sufficient number of squares we can, in a small stove, develop a heat strong enough to cook eggs or to prepare beef-tea. The construction of hot-houses is founded on the observation of these phenomena, the knowledge of which remounts to a remote epoch, but the explanation of which was reserved for modern physics.

Terrestrial or Central Heat.-The temperature of the interior of the earth is in winter always higher than the temperature of the surface. If we take, for example, the air which has penetrated into caves or still deeper cavities, and make it ascend by proper channels into the interior of houses, we shall be able in fact to mitigate the rigour of the cold, although in a very limited manner. In some mills driven by water, for the purpose of preventing the moving power from freezing, and the motion of the wheels from being stopped, it is usual to pass a stream of water through the earth before it reaches the sluice; this water is heated in its subterranean passage, and prevents the cold water with which it is mixed from freezing in the water-course which supplies the mill. This mode of warming is the most economical that can be imagined; but unfortunately its applications are of too limited an extent. includes, however, the germ of a principle which should create an immense revolution in our means of warming buildings. It is well known that the farther we dig into the interior of the earth, the more is the temperature found to be elevated.

It

the mean temperature at the surface to be 10° Centigrade or
50° Fahrenheit, a depth cc, of about 200 feet will give a tem-
perature of 12° Centigrade or 53°-6 Fahrenheit; a depth A A,
of about 1,500 feet will give a temperature of 25° Centigrade
Fig. 227.

or 97° Fahrenheit; and a depth B B, of about 3,000 feet will give a temperature of 38° Centigrade or 100.4 Fahrenheit. In the artesian wells of Grenelle, at the depth of 1,798 feet, the temperature is 27°.8 Centigrade or 82° Fahrenheit.

Various hypotheses have been framed in order to account for the central heat of the globe. That most generally adopted by philosophers and geologists is, that the earth existed at first in a liquid state, by the action of an elevated temperature, and that by radiation the surface was gradually solidified so as to form a solid crust, which is in reality only about 45 miles in thickness, the central mass being still in a liquid state. As to the process of cooling, this can only be extremely slow, on account of the weak conducting power of the terrestrial strata. It is on this account, also, that the central heat does not appear to raise the temperature of the surface of the ground by more than one thirty-sixth part of a degree Centigrade, or onetwentieth of a degree Fahrenheit.

The terrestrial globe, in fact, possesses a heat of its own, which is denominated the central heat. At a depth not very great below the surface, and which varies with the country where the shaft is sunk, we meet with a stratum of earth whose temperature remains the same in all seasons of the year; whence we conclude that the solar heat only penetrates underground to a certain determinate depth. Then, below this stratum, which is denominated the invariable stratum, it is found that the temperature increases at a mean, by 1° Centigrade for every 30 metres deeper that the shaft is sunk; that is, 1° Fahrenheit for every 56 feet. This law of the increase of temperature underground has been verified at great depths in mines and artesian wells. By boring underground to the depth of 3,828 yards, the temperature of the stratum has been found 100° Centigrade, or that of the boiling point of water. The existence of the central heat is confirmed by that of ther-rise in the temperature is from two to three-tenths of a degree; mal springs and volcanoes. As already observed, the depth of the invariable stratum is not the same at all points on the earth's surface. At Paris, it is 29 yards, and the temperature at this depth is constantly the same, namely, 119.8 Centigrade or 530.24 Fahrenheit. Fram the preceding data, we can calculate approximately to what depth it will be necessary to sink a shaft in order to obtain water of a certain degree of heat; and if this water were once brought to the surface, it would be easy to employ it in heating apartments and a variety of other uses, by passing it through pipes to a limited distance. In the following diagram, fig. 227, there is a representation of a section of the interior of the earth to the depth of more than 3,200 feet, showing the interior strata and three artesian wells terminating at different depths, and sending up to the surface water of three different temperatures.

Heat of Molecular Phenomena.-The phenomena of molecular action, such as imbibition and absorption, capillary action, etc., are in general accompanied by the development of heat. M. Pouillet has found that whenever a liquid is poured on a pulverised solid, there is an elevation of temperature which varies according to the nature of the substances. With non-organic matter, such as the metals, the oxides, and the earths, the but with organic matter, such as sponge, farina, starch, liquorice-root, dried membranes, etc., the increase in temperature varies from one to ten degrees. The absorption of gases by solid bodies presents the same phenomenon, M. Dobereiner found that if powdered platinum, such as may be obtained in the state of a chemical precipitate, under the name of Platinum black, be placed in oxygen, this metal will absorb about 250 times its bulk of that gas, and the temperature will then be raised so high as to produce intense combustion. Spongy platinum, which is obtained by precipitating the chloride of platinum with sal-ammoniac (chloride of ammonium), produces the same effect. A jet of hydrogen thrown upon it takes fire by the disengagement of the heat due to the absorption. On this principle is constructed the hydrogen lamp. Supposing This apparatus is composed of two glass vessels, fig. 228.

bituminous or pitchy as to be used for fuel, and it is, on that [5. Sandstone, containing clays and seams of coal, and ironaccount, called, in some places, Kimmeridge coal. It burns stone with vegetable remains. 6. A bed of limestone and dully, with a yellow smoky flame, having a strong smell of sand, corresponding with the interior oolite of the south of pitch. Some suppose that this mass of bituminous matter England. results from the decomposition of vegetables; but others, on account of the bed abounding with marine shells, suppose it to be of animal origin.

In some places the beds contain the sulphate of lime and iron pyrites (pronounced pee-ry-tes). This remarkable circumstance is accounted for by the supposition that the iron pyrites, in decomposing, produces sulphuric acid, or oil of vitriol, which, by uniting with the calcareous or limy matter in the clay, forms the sulphate of lime.

In England these two oolitic beds, A and B, are found only in the southern counties of Wiltshire and Dorsetshire, where they form beds of different thickness, averaging from 70 to 700 feet.

II. THE MIDDLE COLITE.

The strata of the middle oolite consists of gritty imperfect limestone, forming a freestone-very perishable for building materials, as may be seen in several of the older buildings of Oxford. It is full of broken or comminuted shells, and consists, in different places, of from one-tenth to one-third of

sand.

The middle oolite is divided into three beds. 1. The coral rag. 2. The calcareous grit. 3. The Oxford ciny.

C. THE CORAL RAG-The coral rag is a kind of rubbly limestone, formed chiefly by the branching corals called madrepores. This store or rag is called "cors.." because its bed. consists of masses of petrifed corals, wash appear to retain the very position in which they grew at the bottom of These masses of coral rock are somtimes fifteen feet thick. It is used only for burning lime and mending roads. Between the coral rag and the Oxford clay, is found a bed of calcareous or my grit, consisting chiefly of siliceous of flinty sand of a yellowish colour, having in it about one-third

the sea.

of calcareous matter.

At Brora, also, on the east coast of Sutherlandshire, in the north of Scotland, are found shelly limestones with alternations of sands and shales, iron-stones with remains of plants, ferruginous or irony limestone with fossil wood and shells, and sandstones and shales with thin beds of coal.

E. CORNBRASH.-The cornbrash is an imperfect limestone, rough and rubbly, of a brown and earthy appearance. This rock generally separates into thin layers. It is chiefly burned for lime; but occasionally, when masses of considerable thick ness of it are found, it is used for building, as about Malmesbury, in Wiltshire. It has immediately underneath it a bed of blue clay, which is sometimes cf very great thickness, and rests on a siliceous grit-stone.

F. FOREST MARBLE.-The forest marble consists of brownish The more solid beds in this division furnish a stone of suffibeds of argillaceous or clayey limestone, full of marine fossils. cient compactness to receive a polish, and is hence called a marble.

The thin beds afford coarse roofing tiles and rough flagstones,
much used in West Wiltshire and in Somerset. The different
twelve inches in thickness.
lagets are separated by thin seams of clay, from one inch to

Bradford clay, full of organic remains.
The whole rests on a deep bed of marly deposit called the

G. GREAT OOLITE.-The great oolite consists of calcareous beds, having different degrees of compactness and consistency. The softer beds are perfectly oolitic, or consisting of egg-shaped particles; but the harder and more compact beds have less of that roe-like appearance.

The best of these beds supply that beautiful building material called the BATH STONE, which, on account of its softness when taken from the quarry, is capable of every variety of artistical embellishment. St. Paul's Cathedral, in London, is The hills around Bath are composed of it, and the city of Bath built of this stone from a quarry at Burford, in Oxfordshire.

These two beds form a rock of from 100 to 150 feet in thickness; but at Whiteham-hill, in Berkshire, it attains an eleva-is built with it. When in the quarry, the Bath stone is soft

tion of 576 feet.

D. THE OXFORD CLAY.-The Oxford clay is very tenacious, dark blue in colour, but brown on the surface. It forms a bed of great thickness, and contains masses of Septaria, or cement-stone. In some places these Septaria are called Turtlestone; in others, Melbury marble, from a district of that name in Dorsetshire.

and yellowish, but by exposure it becomes hard and white.
H. STONESFIELD SLATE.-The Stonesfield slate is a bed of
limestone of only six feet in thickness, and it is but very
slightly oolitic. It was first known at Stonesfield, near Wood-
stock, in Oxfordshire, and subsequently at Hinton, near Bath,
Colly weston, in Northamptonshire, and the Cleveland Hills,
in Yorkshire. The bed, though thin and limited in extent, is
remarkable for the abundance and the variety of its fossils,
both vegetable and animal.

The quarries at Stonesfield exhibit different fossil beds of buff coloured oolitic limestones, called Pendle, each seam about two feet in thickness; separated by a bed of loose sand called Race of the same thickness. Imbedded in this look like cakes of limestone, from six inches to two feet limestone are concretions called Whimstone, or Potlids. These

In some places the Oxford clay is found combined with bituminous matter, and forms an inflammable shale, like that of the Kimmeridge clay, à circumstance which has led to several abortive attempts at discovering coal. In the lower parts of this clay are remarkable beds of limestone, which is formed almost entirely of one mass of fossil shells. This gingular bed has been called Kelloway rock, on account of its being so well developed at Kelloway-bridge, near Chippenham, The Oxford clay, like the Kimmeridge, contains iron pyrites | in diameter, and often blue in the centre. This cake splits and sulphate of lime; and also, very probably, free sulphur, for when a mass of the clay is burned, it emits a very offensive smell. The well of Melksham Spa, in Wiltshire, which is a sulphureous chalybeate, is sunk in this clayey stratum. same is the case with the springs at Cumor, in Berkshire; Kingscliff, in Northamptonshire; and Stansfield, in Lincolnshire.

in Wiltshire.

The

The bed of the Oxford clay is very deep, and is estimated at 700 feet. At Boston a well was sunk in it to the depth

478 feet.

I. THE LOWER OOLITE.

of

The lower oolites form a very extensive group, consisting of hard rocks with intervening beds of sands and clays. The group of lower oolites is divided into the following beds :1. Cornbrash. 2. Forest marble. 8. Great oolite. 4. Stonesfield slate. 5. Fuilers' earth. 6. Inferior oolite.

In the northern parts of Great Britain the beds differ in lithological character from those of the southern parts. In Yorkshire, as developed on the eastern coast, the division is this: 1. Cornbrash. 2. Sandstones and clays. 3. Shales, with thin layers of coal. 4. Calcareous sand and shelly limestone.

into parallel flakes, and as they separate, their surfaces often expose impressions of shells. The masses of the bed called Pendle are allowed to lie exposed to a winter's frosts, and then, when struck hard on the edge, they also freely split into flakes sufficiently thin to be used for roofing.

At Collyweston, the Stonesfield strata contain some fossil ferns of a species common to the beds of the Yorkshire oolites, where, on the eastern coast, rocks of the bolitic age put on every aspect of a real coal field, and where thin seams of coal Have been actually worked, as in Brora in Sutherlandshire, for many years.

1. FULLERS EARTH.-Under the Stonesfield limestone is a deep bed of clay. In many places this bed of clay is much like Fullers' earth; but at Odd-down, near Bath, the bed is really formed of that earth. It contains partial beds of a rubbly stone of a blue colour. This bed is entirely wanting in the oolites of Yorkshire and Sutherlandshire.

J. INFERIOR QOLIFE.-The inferior oolite, not to be con founded with the phrase "lower oolites," is a calcareous rock, coarse and gritty. It is distinguished from the "great colite" by being much coloured with the red oxide of iron, and by being more mixed with siliceous sand. In its midland