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I am treading upon novel and very uncertain ground; but it is not more against reason, unaided by experiment, to suppose that any body will give off caloric, whether latent or in any other form, on the application of a suitable cause, than to suppose steam, which conveys to our senses or the thermometer a temperature no higher than boiling water, should, on its condensation, give off nearly 1000 degrees more than is contained in boiling water. I say, the one supposition is not more plausible than the other by reasoning simply. Though the one is known from its effects, the other may possibly be explained when our knowledge of the subject becomes more accurate and our instruments more delicate.

On the whole, the increase of temperature on the metal being condensed, and the temperature always being in proportion to the condensation, seem to resemble much the overflowing of a vessel filled to the brim with water, on plunging any body into it; and if the latter fact be a proof of the impenetrability of water, the experiments of Berthollet, if they do not prove the same with regard to caloric, afford, at least, presumptive evidence in its favour.

I come now to consider which of the hypotheses gives the most satisfactory explanation of the phenomena dependent upon caloric. It is a law nearly universal for all matter to expand by the addition of caloric: solids and fluids both observe this law. On this expansion something must enter between the particles, else there must be a vacuum; and on the supposition that there is a vacuum, how does it happen that the atmosphere does not follow its usual law, and rush towards the unoccupied space? If it did enter between the particles of the expanded body, it is natural to suppose that the weight of that body would be increased; but the following experiment of Dr. Fordyce shews that increase of weight does not necessarily follow an increase of temperature. He put 1700 grains of water into a glass globe three inches in diameter, and sealed it hermetically, and then ascertained the weight of the whole. He next plunged the globe into a freezing mixture, where he kept it till part of the water was frozen, which he again weighed; and on comparing the weight of each trial, he found that the frozen water had gained about 1-60th part of a grain. These trials were repeated several times, more of the water being frozen each time, when a corresponding increase of weight was obtained. This would seem to prove that the weight of a body became less on the addition of caloric; and were ponderosity reckoned one of the properties of matter, it would militate against den motexinliter of cloric but as this property is merely relative and

susceptible of change, it cannot upset the idea that caloric is material.

The radiation of caloric is a sufficient proof, were there no other, that it is material. It passes through space in straight lines; it can be reflected at will, and collected into a point, so as to resemble the condensation of bodies confessedly material. It is scarcely possible to conceive that this would arise merely from the commotion of the particles of a body, for the hypothesis implies the greater the commotion the greater is the quantity of caloric; and there is no evidence that the commotion of the particles upon which it is concentrated is greater than those from which it is reflected, unless the increase of temperature be taken as such; besides, the point from which the caloric emanates, and the point upon which it is concentrated, may be under nearly similar circumstances with regard to this agent, yet they must be governed by very different laws: the former being increased in temperature from the commotion of its particles; while, in the latter, the increase of temperature causes the commotion among the particles, or, in other words, what is the cause in one point is the effect in the other.

How ill adapted, then, must the hypothesis be that requires the aid of opposite laws to explain the same phenomena in the same matter! The like reasoning is applicable to the conduction or the communication of caloric from one body to another; but with the idea that caloric is material, the phenomena of radiation and conduction admit of easy explanation.

The hypothesis, also, of its material nature, gives a satisfactory explanation of the phenomena attendant on the conversion of solid substances into fluids or gases, or the reverse: in the former, caloric is absorbed; in the latter, it is given off. How great is the resemblance between this and the absorption of a fluid by a sponge or any porous body, and the escape of that fluid on pressure.

There are, however, some instances in nature, contrary to the general rule, where caloric is produced on the conversion of a body from a smaller to a larger bulk. Of this, the explosion of gunpowder is an example, and which is brought forward against the idea of the material nature of caloric. But the fact proves nothing, save by analogy; and if analogy have any weight, there is as much reason to suspect that caloric, as matter, is lodged among the particles of this astonishing product, ready to burst forth on the application of a suitable cause.

A similar objection may be raised from the fact that water, on

cooling from 40° to 32°, Fah., expands: but this is accounted for on a different principle. It is generally supposed that the crystals which are formed on the water becoming ice, observe a particular arrangement, or that the coaptation among them is not such as to occupy the least possible space. Were this law otherwise, the lakes and streams, in severe winters, particularly in northern regions, would be rendered one complete mass of ice; in short, the fountains of the deep would be dried up, and man would have only a precarious supply of this indispensable requisite. But as it is, water, on cooling from 40° to 32°, expands; it therefore becomes lighter, and swims above the heavier. The particular arrangement of the crystals, as already mentioned, will explain the enlargement without the seeming paradox of matter becoming larger, or matter being extracted.

The only other comparison which I shall draw between the two hypotheses is derived from the production of caloric by percussion or friction; and this, I may add, is reckoned by some as one of the greatest stumblingblocks to the idea that caloric is material.

They argue that whatever can be generated out of nothing cannot be material. Thus, Dr. Young, in his Lectures on Natural Philosophy, says, "If the heat is neither received from the surrounding bodies (which it cannot be without a depression of their temperature), nor derived from the quantity already accumulated in the bodies themselves (which it could not be, even if their capacities were diminished in any imaginable degree), there is no alternative but to allow that heat must be actually generated by friction; and if it is generated out of nothing it cannot be matter, nor even an immaterial or semi material substance." The first of these propositions is admitted, as it can bear the test of experiment; but the second is a mere assumption, viz., “that the caloric cannot be derived from the quantity already accumulated in the bodies themselves, even if their capacities were diminished." Were we able to measure the quantity of caloric in any body, this supposition might be entertained in preference to one more in accordance with the laws of matter. This, however, we cannot do, with our present information; for any body may contain one degree of caloric, or ten thousand, as our knowledge is only relative. Further, the reverse of this assumption will explain all the phenomena attendant on percussion or friction, without the violation of a single law of physics. Whereas the idea that caloric is merely the consequence of motion, for the support of which the assumption is raised, can only be defended by setting aside an important fact in

the laws of motion. For instance, whenever a moving force is applied to any body at rest, part of that force is expended in overcoming the inertia of matter; consequently, the power is less efficient than when the inertia has been overcome. These facts, however, by no means coincide with Berthollet's experiments with the metals, as specified. The first blow, having to overcome the actual or comparative inertia of matter, would naturally, on this view, afford least caloric, as the motion among the particles would be less than on the succeeding blows; but the reverse was the fact, as the first blow afforded the greatest quantity of caloric. That caloric already existing in bodies is merely evolved on percussion or friction, is an assumption as destitute of proof as that which Dr. Young has assumed; but it does not violate any of the known laws of matter, or rather it coincides with some of those laws which the opposite idea directly sets at nought. Therefore, it is certainly more logical to adopt that opinion which is supported by reasons, though not stronger than analogy, in preference to another not only destitute of analogical reasoning, but running directly counter to what analogy might lead us to expect.

The same author remarks that "those who look up with unqualified reverence to the dogmas of the modern schools of chemistry, will probably long retain a partiality for the convenient, but superficial and inaccurate, modes of reasoning which have been founded on the favourite hypothesis of the existence of caloric as a separate substance; but it may be presumed that, in the end, a careful examination of the facts which have been adduced in confutation of that system will make a sufficient impression on the minds of the cultivators of chemistry to induce them to listen to a less objectionable theory." Notwithstanding the denunciation of being a superficial and inaccurate reasoner, I am induced, after taking a retrospect of all the facts connected with caloric, to consider it material. This view gives the most satisfactory explanation of the greater part of the phenomena dependent upon caloric, though a few of them, as instanced in the case of bodies becoming larger and at the same time emitting caloric, may at first stagger us in this belief, yet if we deal with the subject as is done with the other objects of nature, there can be no hesitation about the conclusion I have drawn: I allude to the formation of a law from the general effect of any body, rather than from the exceptions to it.

The invention of the hypothesis that caloric depends on motion, is ascribed to Lord Bacon; and it is supported by the opinions both of

- and Newton. The opinion of such men ought certainly to

make any one pause before he differed from it; but were mere names to be taken as evidence in scientific inquiries, all improvements would fast be at an end. The only legitimate way of interrogating nature is by observation and experiment, and facts fairly deduced from these are of more value than theories the most beautiful, no matter by whose name they are supported.




On the evening of the 15th of December, 1793, a strange and fearful spectacle presented itself from the hill which, on the road from Clisson, overlooks the valley where the village of St. Crepin lies almost hidden among the trees. At first the eye could discover only, in the dim twilight, three or four columns of thick smoke, which, separated at their base, united into one dense mass as they rose, lazily waving in the heavy atmosphere; then rolling away, mixed with the low and foggy clouds. Gradually the dark vapour became more lurid; and at length, bursting from the roofs of the houses, the long forked flames usurped its place with a crackling sound; now, creeping stealthily along; then, darting spirally upwards, piercing the thick mist which hung over them like a mantle. From time to time, as a roof fell in, a more vivid blaze arose, which, mingled with a thousand sparks, disclosed to view a company of soldiers, whose occasional shouts and bursts of merriment contrasted strangely with the awful scene before them. It was a republican brigade of fourteen or fifteen hundred men; who, having found the village deserted, had wantonly set it on fire.

One detached cottage, however, was not yet burning. Every precaution seemed to have been taken to prevent the flames from reaching it. Two sentinels stood at the door, and occasionally an officer or aide-de-camp passed in, and returned to transmit orders to

Clisson, a small town in Bretagne, near Nantes.

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