THE LAW OF SUBSTANCE. 221 



motion of the smallest particles of matter — a vibration 

 of atoms. The atoms themselves, according to the 

 usual "kinetic theory of substance," are dead, separate 

 particles of matter, which dance to and fro in empty 

 space and act at a distance. The real founder and 

 most distinguished representative of the kinetic theory 

 is Newton, the famous discoverer of the law of gravi- 

 tation. In his great work, the Philosophic? Xaturalis 

 Prineipia Mathematica (1687), he showed that through- 

 out the universe the same law of attraction controls 

 the unvarying constancy of gravitation ; the attraction 

 of two particles being in direct proportion to their 

 mass and in inverse proportion to the square of their 

 distance. This universal force of gravity is at work 

 in the fall of an apple and the tidal wave no less than 

 in the course of the planets round the sun and the 

 movements of all the heavenly bodies. Newton had the 

 immortal merit of establishing the law of gravitation 

 and embodying it in an indisputable mathematical 

 formula. Yet this dead mathematical formula, on 

 which most scientists lay great stress, as so frequently 

 happens, gives us merely the quantitative demonstra- 

 tion of the theory ; it gives us no insight whatever 

 into the qualitative nature of the phenomena. The 

 action at a distance without a medium, which Newton 

 deduced from his law of gravitation, and which 

 became one of the most serious and most dangerous 

 dogmas of later physics, does not afford the slightest 

 explanation of the true causes of attraction; indeed, 

 it long obstructed our way to the real discovery of 

 them. I cannot but suspect that his speculations on 

 this mysterious action at a distance contributed not a 

 little to the leading of the great English mathematician 

 into the obscure labyrinth of mystic dreams and 



