MATTER AND FORCE, IN PHYSICAL PHENOMENA. 33 



or is it but an abstraction, an expression for matter 

 under different modes of existence and action ? Or 

 speaking of what are termed forces severally me- 

 chanical, chemical, calorific, electrical, &c. seeing 

 that they are for the most part mutually convertible, 

 and under equivalents of power for this power is never 

 extinguished may there not be some yet undiscovered 

 unity for all, modified by the conditions under which 

 it acts, and possibly including even gravitation and 

 vital force in the one category ? 



Such questions carry us to the extreme verge of 

 physics, if not indeed beyond. They have perplexed 

 schools of philosophy in every age, and inevitably so. 

 Matter, the substratum of all that is present to the 

 senses, is seen at every moment to undergo changes 

 from powers, of which the senses give us no cogni- 

 sance. What are these unseen forces call them 

 Svvdp'is, evepyeia., vis viva, potential energy, plastic 

 force, Krafte, or whatever the diversities or the impo- 

 tence of language may suggest which thus give move- 

 ment and change to the material world ? What is the 

 matter itself, thus acted upon? Is it something 

 brought into existence by a Creative Will of higher 

 date or is it eternal in itself, and that with which the 

 Creator worked in evolving and giving laws to the 

 visible universe ? The questions thus denoted struck 

 the ancient philosophers as they do us, and were 

 answered with greater audacity from the absence of 

 those checks which inductive science imposes. The 

 terms TO 7rdfr%ov and TO TTOIQW briefly express the 

 groundwork of the problem in the Greek philosophy. 



