Modes of Physical Force. 1 09 



The idea is one which excludes anything like that of 

 correlation with electricity or any other force which 

 has nothing whatever to do with any change of the 

 nature of induction more especially, for if it had it might 

 be difficult to avoid the conclusion that the force of 

 gravity is in some way connected with a force of repul- 

 sion, and that there might be a very intimate connexion 

 between electro-magnetic movements and those move- 

 ments in the production of which the force of gravity is 

 held to have so much to do. These are questions, how- 

 ever, which may perhaps be entertained at the end of 

 this volume in a supplement, but which are out of place 

 now, where it must suffice to have noticed that the force 

 of gravity is obedient to the same law as that which 

 rules all other attractive forces, and that it seems to be 

 correlated with light and heat and chemical affinity and 

 electricity and magnetism in the very closest manner. 



More might easily be said upon the correlation of 

 the physical forces, but not without venturing further 

 than I am prepared to go : and I therefore bring my 

 remarks to a close abruptly by simply saying that the 

 idea of unity underlies that of correlation, and that, so 

 far as I can see, the two ideas must stand or fall 

 tosrether. 



