5. On the changes of temperature produced by the rarefaction and condensation of air

In order to estimate with greater accuracy than has hitherto been done the quantities of heat evolved or absorbed during the conden­sation or rarefaction of atmospheric air, the author contrived an apparatus where both the condensing pump and the receiver were immersed in a large quantity of water, the changes in the tempe­rature of which were ascertained by a thermometer of extreme sensibility. By comparing the amount of force expended in condensing air in the receiver with the quantity of heat evolved, after deducting that which was the effect of friction, it was found that a mechanical force, capable of raising 823 pounds to the height of one foot, must be applied in the condensation of air, in order to raise the tempe­rature of one pound of water one degree of Fahrenheit’s scale. In another experiment, when air condensed in one vessel was allowed to pass into another vessel from which the air had been exhausted, both vessels being immersed in a large receiver full of water, no change of temperature took place, no mechanical power having been developed. The author considers these results as strongly corro­borating the dynamical theory of the nature of heat, in opposition to that which ascribes to it materiality; but he reserves the further discussion of this question to a future communication, which he hopes soon to present to the Royal Society.