114 THE REALITIES OF MODERN SCIENCE 



but its amount remains unchanged. Matter may 

 change its form, being solid, liquid or aeriform. We 

 cannot, however, either create or destroy matter. Nor 

 are there any processes of nature whereby it may 

 be done. It may undergo transformations, appear- 

 ing to us now as one chemical substance and now as 

 another, but the total amount of matter in the uni- 

 verse remains unaltered. 



Matter and Energy, two indestructibles of the uni- 

 verse, are the entities in terms of which we must ex- 

 plain all physical phenomena. They are the realities 

 of modern science. In connection with the first, we 

 must always bear in mind the granular and electrical 

 composition. In connection with the second, we shall 

 need a further law as to availability. Some ideas as 

 to this have been given in this chapter. A general 

 statement is contained in what is known as the ' l Second 

 Law of Thermodynamics." Thermodynamics, as a 

 division of science dealing with the forces due to heat, 

 was established before scientists appreciated the unity 

 of physical science. Its first law, embodying the rela- 

 tion which was discovered by Joule, is essentially the 

 principle of the conservation of energy. Its second law 

 states the limits of the availability of energy. 



To-day we realize that these laws are not limited 

 in their application to a particular division of science 

 but are fundamental. In fact, it would be preferable 

 if they could be spoken of as the first and second laws 

 of Energy, but we must use the names which were 

 attached to them at the time they were formulated. 



