Mr. Ivory's Investigation of condensed Heat. 89 



12, for /i' read h. The subsequent formula, in line 14, will 

 then be accurate: but the cases mentioned in page xxv re- 

 quire a slight correction, and should be as follow : 

 Case 1. Arg. = Feb. 10 + (-500 — -378) = Feb. 10-122 



Case 2. Arg. = Feb. 10 + ('750 - -378) = Feb. 10-372 



Case 3. Arg. = Feb. 10 + (-250 — -378) = Feb. 9-872 



Case 4. Arg. = Feb. 10 + (-125 - -378) + -018= Feb. 9-765 

 This error has likewise led to the inaccurate expression x — I 

 in pages xxii line 18, xxiii line 9, xxiv lines 1 and 5, and 

 xxv line 10; in each of which places it ought to be j; + /. 



It is evident that this error will not affect the argument of 

 the Tables, when they are used in this country, or at any of 

 the observatories in the neighbouring states. But, as it might 

 probably mislead a computer under a more distant meridian^ 

 unless previously detected, I have taken the earliest oppor- 

 tunity of making the error known; although it is manifest 

 that the effect will seldom be of much importance. 



Jan. 23, 1827. Francis Baily. 



XXI. Investigation of the Heat extricated from Air isohen it 

 undergoes a given Condensation. By J. Ivory, Esq. M.A. 

 F.E.S.* 



/CONCEIVE a quantity of air confined in a close vessel, 

 ^^ and let heat be applied to it, the pressure remaining in- 

 variable, till it is expanded to a given volume. Again, taking 

 the same mass of air in its first state, let the dimensions of the 

 vessel be suddenly enlarged till the air has acquired the same 

 volume to which it was before expanded by heat: the air 

 •within the vessel will become colder, and after a short mo- 

 ment of time will resume its first temperature. We must 

 therefore infer that air, when its volume is increased, absorbs 

 heat, which occasions the coldness ; and that the coldness dis- 

 appears because the loss of temperature is supplied by the 

 communication of heat from the surrounding bodies. That 

 this is a true account of the matter, and that no heat is lost, 

 it is easy to prove ; for if the vessel containing the expanded 

 air be reduced to its original bulk, the heat before absorbed 

 will be extricated as the air contracts, producing a rise of 

 temperature which is soon dissipated. Now let heat be 

 applied to the expanded air, while its volume is kept from 

 changing, till the temperature is raised to the same degree as 

 in the first operation : it it evident that the air will now be in 



* Communicated by the Author. 

 New Series. Vol. I. No. 2. Feb. 1827. N the 



