40 HABIT AND INTELLIGENCE. [chap. 



of an electric current are due to the charge of magnetic 

 energy which, as I have endeavoured to prove, is obtained 

 by the transformation of the energy of the electric current, 

 and taken up and, as it were, for the time incorporated 

 with the iron.^ 'None of these forces are primary forces, 

 because the bodies have acc[uired them and may lose 

 them. 

 Three pri- There are three, and only three, kinds of primary force, 

 forces These are : 1, Gravity ; 2, Capillary attraction ; and, 3, the 

 gravity, attraction of chemical elements that seek to combine (as, 

 and\fii- ^' fo^ instance, oxygen and hydrogen, or oxygen and carbon), 

 ^^^y- or, to use the common but very infelicitous term, chemical 



affinity. For the sake of brevity let us call these gravity, 

 capillarity, and affinity. Capillarity is of much less im- 

 portance than the other two, but I mention it in order to 

 make the enumeration complete. 

 Their pro- Gravity acts at all distances, and is for that reason a 

 per les. f^xce acting on masses — a molar force. Capillarity acts 

 only at insensible distances ; in other words, it acts only 

 when bodies are in immediate contact. It is for that 

 reason a force acting on molecules — a molecular force. 

 Affinity also acts only at insensible distances ; but there 

 is this difference between capillarity and affinity, that 

 capillarity acts on the molecules into which a body may 

 be broken up by mere mechanical division, while affinity 

 acts on the chemical atoms which are the constituent parts 

 of the molecules. Affinity is consequently an atomic 

 force. 2 



Gravity, acting at all distances, is, probably for that 

 reason, always in action — all matter is always attracting 

 all other matter. Capillarity and affinity, acting only 

 at insensible distances, act, probably for that reason, 

 only under favourable circumstances ; capillarity is chiefly 



J See Note to Chapter III. 



2 When I speak of molecules and atoms, I only mean the smallest 

 integrant and constituent parts, without implying any opinion as to 

 whether or not these are infinitely small. I speak of the molecules of a 

 body in the same way that mathematicians speak of infinitely, or inde- 

 finitely, small arcs of a curve. 



