SOME UNSOLVED SCIENTIFIC PROBLEMS 



ago, but for two or three generations remained prac- 

 tically unnoticed. The philosophers of the first half of 

 our century seem to have despaired of explaining gravi- 

 tation, though Faraday long experimented in the hope 

 of establishing a relation between gravitation and elec- 

 tricity or magnetism. But not long after the middle of 

 the century, when a new science of dynamics was claim- 

 ing paramount importance, and physicists were striving 

 to express all tangible phenomena in terms of matter in 

 motion, the theory of Le Sage was revived and given a 

 large measure of attention. It had 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 concep- 

 tion based, like most other physical speculations of the 

 last generation, upon the hypothesis of the vortex atom, 

 and was suggested, no doubt, by those speculations 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 gravitation 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. According to this view, gravi- 

 tation is not a push from without, but a pull from within ; 

 not due to exterior influences, but an inherent and indis- 

 soluble property of matter itself. The conception has 

 the further merit of correlating gravitation with elec- 

 tricity, 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 



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