A HISTORY OF SCIENCE 



seemed to have at least the merit of explaining the 

 facts without conflicting with any known mechanical 

 law, which was more than could be said of any other 

 guess at the question that had ever been made. 



More recently, however, another explanation has 

 been found which also meets this condition. It is a 

 conception based, like most other physical speculations 

 of the last generation, upon the hypothesis of the vor- 

 tex atom, and was suggested, no doubt, by those spec- 

 ulations which consider electricity and magnetism to 

 be conditions of strain or twist in the substance of the 

 universal ether. In a word, it supposes that gravita- 

 tion also is a form of strain in this ether a strain that 

 may be likened to a suction which the vortex atom is 

 supposed to exert on the ether in which it lies. Ac- 

 cording to this view, gravitation is not a push from 

 without, but a pull from within; not due to exterior 

 influences, but an inherent and indissoluble property 

 of matter itself. The conception has the further merit 

 of correlating gravitation with electricity, magnetism, 

 and light, as a condition of that strange ethereal ocean 

 of which modern physics takes so much account. But 

 here, again, clearly, we are but heaping hypothesis 

 upon hypothesis, as before. Still, an hypothesis that 

 violates no known law and has the warrant of philo- 

 sophical probability is always worthy of a hearing. 

 But we must not forget that it is hypothesis only, not 

 conclusive theory. 



The same caution applies, manifestly, to all the other 

 speculations which have the vortex atom, so to say, for 

 their foundation-stone. Thus Professors Stewart and 

 Tait's inferences as to the destructibility of matter, 



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