DIVISIBILITY OP MATTER ATOMIC THEORY. 77 



motion either constitute this power, or are pervaded 

 by and give conduction and other action to it. With 

 the view I entertain of the relation of electricity to the 

 ether of space of which I shall speak more in another 

 paper I think the latter the more probable interpre- 

 tation. The phenomena of electricity in vacuum-tubes 

 show the exquisite tenuity to which air and other 

 vapours must be reduced before they cease to give 

 passage to the electric current. 



Of gravitation in its connexion with the atomic 

 theory I have spoken in another of these papers. We 

 may describe it as a property inherent in all matter, 

 but such phrase adds nothing real to our knowledge 

 of this great force, gives no conception of its origin in 

 individual atoms, of the aggregation of units of force, 

 or of its transmission through space. The relation of 

 the ponderable to the imponderable, of matter to the 

 powers acting upon it, forms indeed that mysterious 

 volume which science has opened, but has not yet been 

 able adequately to decipher. 



Although the doctrine of atoms was a mere specu- 

 lation in ancient philosophy, yet, even as such, it is 

 worth noting how far human thought, working by 

 itself, advanced towards those conclusions which have 

 become the recognised truths of our own day. With- 

 out recurring to the doctrines, so often quoted, of 

 Anaxagoras, Democritus, Epicurus, &c., or to the great 

 poem of Lucretius which gives so magnificent a frame- 

 work to all atomic speculations, it is enough to say 

 that we find pervading the most remote philosophical 

 antiquity a general notion of indivisible, indestructible 



