568 PROFESSOR WILLIAM THOMSON'S ACCOUNT OF 



51. The expression for the amount of work necessary to produce a unit of 

 heat is 



E 



and therefore Regnault's experiments on steam are available to enable us to cal- 

 culate its value for any temperature. By finding the values of /x at 0\ 10', 20 , 

 kc, from Table I., and by substituting successively the values 0, 10, 20, &c., for 

 t, the following results have been obtained. 



Table of the Values of — — p -, 



E 



Mr Joule' f; experiments were all conducted at temperatures from 50 to 

 about 60 Fahr., or from 10' to 16° cent. ; and, consequently, although some irre- 

 gular differences in the results, attributable to errors of observation inseparable 

 from experiments of such a very difi&cult nature are presented, no regular depend- 

 ance on the temperature is observable. From three separate series of experi- 

 ments, Mr Joule deduces the following numbers for the work, in foot-pounds, 

 necessary to produce a thermic unit Fahrenheit by the compression of a gas. 



820, 814, 760. 

 Multiplying these by 1-8, to get the corresponding number for a thermic unit 



centigrade, we find 



1476, 1465, and 1368. 

 The largest of these numbers is most nearly conformable with Mr Joule's 

 views of the relation between such experimental " equivalents," and others which 

 he obtained in his electro-magnetic researches ; but the smallest agrees almost 

 perfectly with the indications of Carnot's theory ; from which, as exhibited in 

 the preceding Table, we should expect, from the temperature in Mr Joule's expe- 

 riments, to find a number between 1369 and 1379 as the result. 



