One difficulty seems to have occurred to M. M. Dulong and Petit. They all along conceive that the specific heats of bodies, that is, the heats producing equal increments of temperature, must necessarily be proportionate to their whole heat. This is purely hypothetical, till established by experiment. The generality of writers on specific heat had conceived it almost confirmed by experiment. The results of Delaroche and Berard have shewn that in elastic fluids the increments of heat are not proportional to the whole quantities, but on the contrary are less when a body is elastic than when liquid. Indeed some writers have argued this should be the case; because a body nearly saturated with another has less affinity for it left.[27] It is plain then that oxygen gas or any other elastic fluid, may have a small specific heat in the sense above defined, and yet have an almost unlimited quantity of heat. I am not aware of any one established fact that does not admit of an explanation upon the hypothesis that heat exists in definite quantities in all bodies, and is incapable of any change, except perhaps into one of the other equally imponderable bodies, light or electricity. [Footnote 27: See Dr. Henry’s note, Manch. Memoirs, vol. 5, page 679.] NEW TABLE OF THE _Forces of Vapours in Contact with the Generating Liquids at Different Temperatures._ (A) = Temperatures by the common thermometer. (B) = Ether vapour, ratio 2 Spec. Gravity .72 (C) = Sulphuret of carbon vapour, ratio 1.978 (D) = Alcohol vapour, ratio 2.7 Spec. Gravity .82 (E) = Acetic acid vapour, ratio 2.57 (F) = Water, ratio 2.602() -----+--------+--------+--------+--------+------- (A) | (B) | (C) | (D) | (E) | (F) -----+--------+--------+--------+--------+------- | Inches | Inches | Inches | Inches |Inches | of M. | of M. | of M. | of M. | of M. -----+--------+--------+--------+--------+------- 7° | 3.75 | 3.134 | .193 | | .11 35 | 7.5 | 6.20 | .560 | .27 | .29 65+ | 15. | 12.26 | 1.51 | .69 | .75 97 | 30 | 24.26 | 4.07 | 1.77 | 1.95 133 | 60 | 48. | 11.00 | 4.54 | 5.07 173 | 120 | | 29.70 | 11.7 | 13.18 220 | 240 | | 80.2 | 30. | 34.2 272 | | | | | 88.9 340 | | | | | 231 -----+--------+--------+--------+--------+------- This is an improved and extended table of the force of vapour, similar to that at page 14, vol. I. It shews that the different vapours increase inforce in geometrical progression, to certain intervals of temperature, the same to most or all liquids. These intervals of temperature were presumed in the former table, to be in reality _equal_ to one another; but the accuracy of this last notion has been questioned.