. Annals of Philosophy. 819.] and on the Laws of the Communication of Heat. First Case.—Thermometer in its natural state. 323 Excess of Ihe tem- perature of the thermometer. Total velocities of the cooling of the ther uiometer. 80° 60 40 20 22-96° 16-14 9-87 4-28 Velocities of cool- ing in vacuo. 5-03° 3-54 2-18 0-95 Velocity of cooling due to the gas. 17-93° 12-60 7-69 3-33 Excess of the tem- perature of the thermometer. Total velocities of the Veloci,ics of coo, coolmg of the ther-, inff |n vacuo> Velocities of cool- ing due to the gas. This comparison gives for hydrogen a resul
. Annals of Philosophy. 819.] and on the Laws of the Communication of Heat. First Case.—Thermometer in its natural state. 323 Excess of Ihe tem- perature of the thermometer. Total velocities of the cooling of the ther uiometer. 80° 60 40 20 22-96° 16-14 9-87 4-28 Velocities of cool- ing in vacuo. 5-03° 3-54 2-18 0-95 Velocity of cooling due to the gas. 17-93° 12-60 7-69 3-33 Excess of the tem- perature of the thermometer. Total velocities of the Veloci,ics of coo, coolmg of the ther-, inff |n vacuo> Velocities of cool- ing due to the gas. This comparison gives for hydrogen a result similar to that for air. The equality being thus verified for surfaces differing so much from each other as glass and silver, and for gases of such different qualities as air and hydrogen, it is natural to generalize the result, and to deduce from it the following law. The loss of heat owing to the contact of a gas, other things being equal, is independent of the state of the surface of the body which cools. This remarkable law of the communication of heat has been already admitted by Mr. Leslie. But this skilful philosopher has only given it as a probable consequence of two indirect experi- ments, which consist in proving that the state of the surface has only a very feeble effect on the time of cooling in those circum- stances in which radiation can contribute but a very small por- tion of the loss of heat. This is the case, for example, when a hot body is exposed to a violent wind, or when it is plunged into a liquid. But these experiments, however ingenious, can never completely supply the place of direct observations. And in the present case would it not have been possible, for example, to suppose that a property observed in air while violently in motion, could only be applied in a limited sense to air in a state of rest ? This doubt would appear still better founded, or would be changed into certainty, if we admitted with Mr. Leslie that air in a state of rest dep
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