the Rarefaction aftd Condensatioti of Air. 375 



milar to the last, except in the extent to which the compression 

 of the air was carried. 



Table II. 



After applying the proper correction for the increase of 

 friction during condensation, and reducing the result, as 

 before, to the capacity of a lb. of water, I find 5°'26 to be the 

 mean quantity of heat evolved by compression of air in the 

 above series of experiments. 



The mechanical force spent in the condensation is repre- 

 sented in this instance by 



s = 1779-3 X 2-302585 x log 10-498 = 4.183-46. 



Hence the equivalent of a degree of heat per lb. of water, 

 as determined by the above series, is 795 lbs. raised to the 

 height of one foot. 



The mechanical equivalents of heat derived from the fore- 

 going experiments were so near 838 lbs.*, the result of mag- 

 netical experiments in which "latent heat" could not be sus- 

 pected to interfere in any way, as to convince me that the heat 

 evolved was simply the manifestation, in another form, of the 

 mechanical power expended in the act of condensation : I was 

 still further confirmed in this view of the subject by the fol- 

 lowing experiments. 



I provided another copper receiver (E, fig. 3) which had a 

 capacity of 134 cubic inches. Like the former receiver, to 



• Phil. Mag. S. 3. vol. xxiii. p. 441. 



