170 Mr. Ivory's Notice relathig to the 



in combining with matter never changes its nature ; it is never 

 annihilated ; it passes from free heat to latent heat, and the 

 contrary, according to circumstances. The only question is 

 about the generality of the fact ; whether it be true that heat 

 which expands bodies is always concealed from the thermo- 

 meter. We have proved that it is true in elastic fluids ; and 

 analogy, aided by the discoveries of Dr. Black, affords a strong 

 argument that it holds without exception. 



The theorv we have been explaining is nowise inconsistent 

 with the doctrine of specific heat and capacity. We have here 

 compared the quantities of heat which unite with bodies when 

 their temperatui-e is raised, with the dilatation which they 

 produce. But we may likewise compare with one another the 

 quantities of heat requisite to cause a given rise of tempera- 

 ture in different bodies ; and, in this view, they are called 

 specific heats, and the bodies themselves are said to have dif- 

 ferent capacities for heat. These two ways of considering 

 the manner in which heat combines with bodies, are clearly 

 distinguished. The one by no means supersedes the other. 

 On the contrary, we may deduce from the property of latent 

 heat we have endeavoured to establish, the condition which 

 causes the capacity of a body to be constant, or to vary. 

 Whenever equal additions of latent heat produce equal incre- 

 ments of volume, the capacity must be constant ; otherwise it 

 must vary. This will readily appear, if it be considered that 

 it is the latent heat which causes the expansion, and that we 

 employ the expansion to measure the free heat, or the tem- 

 perature. The specific heat of bodies is, therefore, plainly 

 regulated by the latent heat. But in other respects the doc- 

 trine of capacity leads to considerations of which we have had 

 no occasion to speak. 



The observations I have been led to make have carried me 

 far beyond my original intention, and I must reserve what 

 further remains on this subject for a future occasion. 



Feb. 5, 1827. J. Ivory. 



XXXVI. Notice relating to the Seconds Pendulum at Port 

 Bowen. Bij J. Ivory, Esq. M.A. F.E.S* 



T^HE ith part of the Philosophical Transactions just pub- 



-*■ lished, contains an experimental determination of the 



seconds pendulum at Port Bowen, a station in Prince Regent's 



Inlet, by Lieutenant Henry Foster^ R.N. F.R.S. The result 



* Coramunicated by the Author. 



of 



