AND ITS SELF-CONSERVATION. 181 



motion may be imparted or transferred from one body 

 to another, the balance between attraction and repulsion 

 within any given quantity of matter must be constantly 

 undergoing change, and, as a consequence, the volume 

 of any and every body must as constantly undergo 

 variation. 



Let us trace, briefly, some of the consequences of 

 this evident fact of the interrelation between attraction 

 and repulsion. And, first, let us note the special char- 

 acteristics of 



a. HEAT. 



That phase of molecular motion specially manifest in 

 the expansion of bodies, is now named Heat. It is 

 affirmed as a general law in physics that heat expands 

 all bodies. That is, heat is declared to be a mode of 

 repulsion. Thus, the degree of expansion which a given 

 volume of a selected substance undergoes, serves as the 

 measure of intensity of heat. 



In reality the expansion is a measure of the increase 

 of one phase of force, as compared with another, in a 

 given quantity of matter. So that heat, as measured by 

 a thermometer, may be said to be the varying degrees 

 in the intensity of repulsion relatively to attraction; 

 just as weight, far from being identical with gravity, is 

 in reality the measure of the excess of centripetal over 

 centrifugal force. 



It is also worthy of notice, that the "exceptions" 

 to the law that heat expands all bodies, are found to be 

 no exceptions. They are, in fact, due to crystallization. 

 We have already had occasion to notice that the com- 

 plexity of grouping of particles follows upon the com- 



