86 Attraction of Gravitation 



There can be little doubt that the latter is by far the 

 more promising direction of inquiry. For we know that 

 all matter is possessed of eternal energy, whose amount is 

 far more than sufficient to explain all the known effects 

 of gTavitation. Each atom is for ever in motion, and there- 

 fore fraught with its own store of kinetic energy due to 

 this motion, the gross amount of these molecular energies 

 being far beyond any force to which living beings can pre- 

 tend. 



On the other hand, to refer the energy arising from 

 gravitation to energies external to the bodies themselves, 

 is in every way unsatisfactory. Newton at first decHned 

 to speculate on this subject, declaring that there was no 

 known energy external to the bodies to which their result- 

 ing energy could be attributed. Pressed by the importu- 

 nities of his friends, he formed a theory of the causation of 

 gravitation, referring it to supposed external agencies ; but 

 he attaches no value to his speculations, as they are based 

 on the utterly unscientific method of explaining the existence 

 of a known effect, by assuming the existence of an imagi- 

 nary cause invented for the sole purpose of explaining 

 that effect. 



The same objection is open to the theories of Lesage and 

 Mossotti. If we allow to Lesage that the universe is filled 

 with extra-mundane particles, moving at high velocities 

 and impinging on all bodies, and if we allow that these 

 bodies have a cage -like structure, then gravitation may be 

 partly explained ; but an hypothesis which calmly assumes 

 two important propositions, for the purpose of partially 

 explaining a third, introduces more difficulties than it 

 removes. 



In the same way Mossotti requires us to allow, first, that 

 all particles of matter repel one another, which is a gratuitous 

 assumption ; secondly, that all particles of intervening ether 

 repel one another, which is a second gratuitous assumption ; 

 thirdly, that particles of ether and particles of matter 

 attract one another, a third assumption, with this special 

 objection, that it assumes the whole question, when it speaks 

 of attraction between particles. Here, then, we have three 

 assumptions for the purpose of explaining a single fact. 

 The mathematical part of the work is handled in a masterly 

 way ; but just as an equation is not solved, if we introduce 

 unknown quantities and allow them to remain in our final 



