MODERN THOUGHT 141 



coveries in reference to its action in the physical world explain the mo- 

 tions and relations of the heavenly bodies, but it is affirmed confidently 

 that the theory of universal motion or the kinetic theory removes more 

 difficulties in the explanation of the phenomena of the universe than 

 either the astronomical or the atomic theory. In passing, it may be 

 mentioned that this theory of universal motion was taught not only 

 by Heraclitus, but by Anaxagoras of Athens, who saw that with his 

 well-nigh innumerable germs he could not solve the problems of the 

 universe apart from motion, and therefore introduced into his system 

 of philosophy, the nous, or intelligence, to give the first push to matter 

 and impart to it the movement which he believed to be universal and 

 without which life could not exist. 



The fourth of the abstract theories employed to explain the uni- 

 verse is the physical theory or the theory of energy. By this theory 

 we understand that whatever is or has come to be has been caused by 

 the force or energy there is in matter. The astronomical theory fails 

 to account satisfactorily for molecular activity and chemical affinity: 

 the kinetic theory is set aside because it is based on dualism or the 

 existence of matter and ether. What is true in these theories is pre- 

 served and the difficulties found in the application of each one of them 

 are avoided by the use of the general term energy, a term under which, 

 according to Young, all that is known in science may be expressed. 

 Energy or force is that something in nature which can do work and 

 be stated in terms of horse power. We speak of latent energy, of 

 energy created by friction, by the fall of water, by steam, and, although 

 we are unable to define it, we describe it as something everywhere 

 present and able, when properly harnessed or directed, to do a certain 

 amount of work. 



While refusing to speak of energy as a property of matter and 

 denying that it is matter in any true sense of the word, it is affirmed 

 that its amount in the material world can neither be increased nor 

 diminished, that while from a heated object a certain portion of heat 

 departs in cooling, a fact which is described as entropy, the sum total 

 of energy, whether in the form of heat or of some other force, remains 

 the same. This truth is set forth by Helmholtz as the conservation of 

 force, a doctrine which, while admitting that a particular form of 

 energy may be changed into another form, affirms that the energy 

 itself is neither destroyed nor diminished by the transformations 

 through which it may pass. Energy is valueless unless capable of 

 transformation. It is good for nothing till it is made usable. Hence 

 the study of energy has been more constantly directed toward discov- 

 ering methods by means of which its power may be employed for the 

 welfare of mankind, than toward ascertaining its nature. We know 

 that energy may be changed in form, that it now appears as heat, now 

 as light, now as electricity, now as magnetism. Nor are these the only 



