ACHILLES AND THE TORTOISE. 



the various phenomena of what we call the 

 different elements and compounds are due to 

 differences in the groupings, arrangements, and 

 vibrations of the ultimate particles of which 

 matter consists. Thus we know that colour is 

 a question of texture. Chemical composition 

 is largely a question of grouping and arrange- 

 ment. Heat, light, electricity, and gas-pressure 

 are questions of vibration. Magnetic attrac- 

 tion, frequently a manifestation of electric 

 energy, is therefore a question of vibration. 

 Possibly also the attraction of gravitation it- 

 self is another question of special forms of vibra- 

 tion ; and it may be that, as changes in the 

 condition of iron can vary the degree in which 

 it is the seat of magnetic attraction, so changes, 

 not at present under our control, in the vibra- 

 tions of the ultimate particles may vary the 

 degree in which they are the seat of the energy 

 of gravitation that is, may change the weight 

 of objects. 



We know also that matter can influence other 

 matter in its neighbourhood. Heat, light, elec- 

 tricity, and magnetism are all cases which 

 exhibit the energy of matter displaying this 

 tendency, which often takes the form of a 

 tendency of the special kind of energy to re- 

 produce itself in surrounding matter; and 

 these manifestations often show themselves in 

 definite relation to local direction. 



( It is quite conceivable, therefore, that what 



285 



