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III. Investigations of the Specific Heat of Solid Bodies. 
By Hermann Kopp. Communicated by T. Graham, Esq., F.B.S. 
Received April 16, — Read May 12, 1864. 
I. Historical Introduction. 
I. About the year 1780 it was distinctly proved that the same weights of different 
bodies require unequal quantities of heat to raise them through the same temperature, 
or on cooling through the same number of thermometric degrees, give out unequal quan- 
tities of heat. It was recognized that for different bodies the unequal quantities of heat, 
by which the same weights of different bodies are heated through the same range, must 
be determined as special constants, and considered as characteristic of the individual 
bodies. This newly discovered property of bodies Wilke designated as their specific 
beat , while Crawford described it as the comparative heat, or as the capacity of 
bodies for beat. I will not enter upon the earliest investigations of Black, Irvine, 
Crawford, and Wilke, with reference to which it may merely be mentioned that 
they depend essentially on the thermal action produced when bodies of different tem- 
peratures are mixed, and that Irvine appears to have been the first to state definitely 
and correctly in what manner this thermal action (that is, the temperature resulting 
from the mixture) depends on the original temperature, the weights, and the specific 
heats of the bodies used for the mixture. Lavoisier and Laplace soon introduced the 
use of the ice-calorimeter as a method for determining the specific heat of bodies ; and 
J. T. Mater showed subsequently that this determination can be based on the observa- 
tion of the times in which different bodies placed under comparable conditions cool to 
the same extent by radiation. The knowledge of the specific heats of solid and liquid 
bodies gained during the last century, and in the first sixteen years of the present one, 
by these various methods, may be left unmentioned. The individual determinations 
then made were not so accurate that they could be compared with the present ones, 
nor was any general conclusion drawn in reference to the specific heats of the various 
bodies. 
2. Dulong and Petit’s investigations, the publication of which commenced in 1818, 
brought into the field more accurate determinations, and a general law. The investiga- 
tions of the relations between the specific heats of the elements and their atomic weights 
date from this time, and were afterwards followed by similar investigations into the rela- 
tions of the specific heats of compound bodies to their composition. In order to give a 
general view of the results of these investigations, it is desirable to present, for the ele- 
ments mentioned in the sequel, a synopsis of the atomic weights assumed at different 
MDCCCLXV. M 
