On the Materiality of Caloric. 617 
between’ the terms’ affinity and capacity is not’ 
merely a verbal one; but that they are actually: 
expressive ‘of different’ powers or catises: and 
the question, therefore, which ‘of> these terms 
shall be adopted, in the description: of facts, is 
one involving the determination of catises. 
The term capacity for heat ‘is employed, by 
Dr. Crawford and others, to denote, in the 
abstract, that power, by which different kinds 
of matter acquire different quantities of caloric. 
But in the various applications, that are made of 
this theory, a more precise Meaning is often 
affixed to it; and the term is applied, in much 
the same sense, which it has in common lan- 
guage. When thus understood, a difference of 
Capacity necessarily implies a difference in the 
extent .of the spaces, ‘between the minute par- 
ticles of bodies; and that these differences occa- 
sion the varieties, observed in the acquirement 
of heat. by -different bodies. On ‘this theory, 
there is no active principle or power inherent 
in bodies, and: more’ active in» some’ than. in 
others,—no tendency in the matter: of heat to 
attach itself, in preference, ta any one .sub- 
stance. The assigned cause. of the phenomena 
of heat is not, I apprehend, adequate to pra. 
duce the effects as d to it, | 
On the theory capacities, a change of 
form is, in certain instances, antecedent to the | 
