Call it insensible caloric, and the difficulty will appear much less formidable. It is indeed a sort of contradiction to call it heat, when it is so situated as to be incapable of producing that sensation. Yet this modification of caloric is commonly called SPECIFIC HEAT. CAROLINE. But it certainly would have been more correct to have called it _specific caloric_. EMILY. I do not understand how the term _specific_ applies to this modification of caloric? MRS. B. It expresses the relative quantity of caloric which different _species_ of bodies of the same weight and temperature are capable of containing. This modification is also frequently called _heat of capacity_, a term perhaps preferable, as it explains better its own meaning. You now understand, I suppose, why the milk and chalk required a longer portion of time than the lead to raise their temperature to that of the oven? EMILY. Yes: the milk and chalk having a greater capacity for caloric than the lead, a greater proportion of that fluid became insensible in those bodies: and the more slowly, therefore, their temperature was raised. CAROLINE. But might not this difference proceed from the different conducting powers of heat in these three bodies, since that which is the best conductor must necessarily attain the temperature of the oven first? MRS. B. Very well observed, Caroline. This objection would be insurmountable, if we could not, by reversing the experiment, prove that the milk, the chalk, and the lead, actually absorbed different quantities of caloric, and we know that if the different time they took in heating, proceeded merely from their different conducting powers, they would each have acquired an equal quantity of caloric. CAROLINE. Certainly. But how can you reverse this experiment? MRS. B. It may be done by cooling the several bodies to the same degree in an apparatus adapted to receive and measure the caloric which they give out. Thus, if you plunge them into three equal quantities of water, each at the same temperature, you will be able to judge of the relative quantity of caloric which the three bodies contained, by that, which, in cooling, they communicated to their respective portions of water: for the same quantity of caloric which they each absorbed to raise their temperature, will abandon them in lowering it; and on examining the three vessels of water, you will find the one in which you immersed the lead to be the least heated; that which held the chalk will be the next; and that which contained the milk will be heated the most of all. The celebrated Lavoisier has invented a machine to estimate, upon this principle, the specific heat of bodies in a more perfect manner; but I cannot explain it to you, till you are acquainted with the next modification of caloric. EMILY. The more dense a body is, I suppose, the less is its capacity for caloric? MRS. B.