Mr. Joule's experiments were all conducted at temperatures from 50° to about 60° Fahr., or from 10° to 16° Cent.; and consequently, although some irregular differences in the results, attributable to errors of observation inseparable from experiments of such a very difficult nature, are presented, no regular dependence on the temperature is observable. From three separate series of experiments, 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 experiments, to find a number between 1369 and 1379 as the result.[1]
- ↑ The best figure (1896) is J = 778 ft.-lbs. = 1 B.T.U., or J = 426.8 kgm. = 1 calorie, and probably with great accuracy.
