564 PHILOSOPHICAL THOUGHT. 



perhaps by mathematicians and mathematical physicists, 

 that the manner in which they defined and used the 

 terms matter and force was quite different from the 

 conception of these things in common life and practice. 

 In fact, it took a very long time before, even in the 

 better text-books of physical science, not to speak of 

 those of chemistry and biology, clear definitions were 

 introduced. 



In the many editions of Biichner's work which ap- 

 peared during the second half of the nineteenth century, 

 nothing is more evident than the change which has 

 come over the meaning of such words as matter and 

 force in the minds of naturalists themselves. The first 

 edition appeared at a time when the conservation of 

 energy was clearly understood only by very few of the 

 foremost representatives of the physical sciences, and in 

 later editions of the book, though the word energy is 

 occasionally introduced, there is no explanation of the 

 reasons which brought about the change of terminology. 

 Also the book appeared at a time when the notion of 

 action at a distance still appeared as an axiom in most 

 of the scientific works published on the Continent. 

 Helmholtz had, in the year 1847, published his cele- 

 brated tract on the ' Conservation of Force,' which, 

 through its very title, perpetuated the vagueness which 

 still adhered to the term. He also, characteristically 

 of the school in which he was brought up, advanced 

 the proposition that natural phenomena might be con- 

 sidered to be fully explained if they were reduced to 

 attracting and repelling forces acting between particles 

 at a distance. It was the ase that was content with 



