418 
SECOND report-1832. 
us to decide at once on the second series of differences, which re¬ 
fer to the multiples and submultiples of the true atomic weights. 
Many chemists, and, among others, Berzelius and Dr. Thom¬ 
son, have adopted the law above enounced; and the latter has 
employed it as an argument in fixing upon the weights of hy¬ 
drogen, gold, copper, and some other simple substances*. Still 
the theory cannot be considered so well established as not to re¬ 
quire that further experiments should be made, and especially 
that it should be rigorously determined whether or not the law 
hold also in regard to compound bodies. 
Among the experiments lately undertaken with the view of 
trying the results of Dulong and Petit, those of Mr. Potter, 
an ingenious and zealous member of this Association, cannot 
have escaped the attention of persons who have interested 
themselves in this subject. The results of these experiments 
are detailed in two papers in Dr. Brewster’s Journal f, the 
second containing a series of corrections upon those in the first. 
The former results of Mr. Potter led him to a confirmation of 
the law; the latter induce him to consider it “ not capable of 
proof;” but a further consideration of certain objections he has 
advanced against it may probably incline him to modify this 
opinion. 
In confirmation of the law, results have been obtained by 
various experimenters. Weber J, by a very ingenious applica¬ 
tion of the change of elasticity and temperature which thin bars 
of metal undergo by a sudden lengthening through mechanical 
agency, has deduced for iron, copper, silver, and platinum, spe¬ 
cific heats which coincide with and extend those of Dulong and 
Petit §. The change of elasticity was measured by the number 
of vibrations in equal times before and after the lengthening, 
and the heats calculated by the known laws of elasticity. 
The specific heats of tin and lead, as determined by Dulong, 
have also been confirmed by a direct experiment of Dr. Erman, 
jun. ||, who obtained a ratio between them differing from his only 
in the fourth decimal place. But the strongest confirmation of 
the law has been derived from the recent elaborate researches 
of Neumann of Konigsberg. 
* Inorganic Chemistry , vol. i. p. 9. 
p N. S. vols. v. and vi. J Poggendorf’s Annalen , vol. xx. p. 177. 
§ Those of Dulong and Weber are as under:— 
Dulong. 
Weber. 
Iron. 
_ -1026 
Copper. 
. -0872 
Silver. 
.... *0525 
Platinum. 
. -0259 
|| Poggendorf’s Annalen, vol. xx. p. 290. Ibid. vol. xxiii. p. 1. 
