PROFESSOR LOVERING'S ADDRESS. 315 



it or through it. According to their view, action at a distance is the 

 force, and it admits of no other illustration, explanation, or analysis. 

 It is not surprising that Faraday and others, who had lost their faith 

 in action at short distances, should have been completely staggered 

 by the ordinary interpretation of the law of gravitation, and that they 

 declared the clause which asserted that the force diminished with the 

 square of the distance to be a violation of the principle of the conser- 

 vation of force. 



Must we, then, content ourselves with the naked facts of gravita- 

 tion, as Comte did, or is it possible to resolve them into a mode of 

 action, in harmony with our general experience, and which does not 

 shock our conceptions of matter and force ? In 1798, Count Rumford 

 wrote thus : " Nobody surely, in his sober senses, has ever pretended 

 to understand the mechanism of gravitation." Probably Rumford 

 had never seen the paper of Le Sage, published by the Berlin Acad- 

 emy in 1782, in which he expounded his mechanical theory of gravi- 

 tation, to which he had devoted sixty-three years of his life. In a 

 posthumous work, printed in 1818, Le Sage has developed his views 

 more fully. He supposed that bodies were pressed toward one another 

 by the everlasting pelting of ultra-mundane atoms, inward bound from 

 the immensity of space beyond, the faces of the bodies which looked 

 toward each other being mutually screened from this bombardment. 

 It was objected to this hypothesis, which introduced Lucretius into 

 the society of Newton and his followers, that the collision of atoms 

 with atoms, and with planets, would cause a secular diminution in the 

 force of gravity. Le Sage admitted the fact. But, as no one knew 

 that the solar system was eternal, the objection was not fatal. As the 

 necessity for giving a mechanical account of gravitation was not gen- 

 erally felt at the time, the theory of Le Sage fell into oblivion. In 

 1873, Sir William Thomson resuscitated and republished it. He has 

 fitted it ont in a fashionable dress, made out of elastic molecules in- 

 stead of hard atoms, and has satisfied himself that it is consistent with 

 modern thermo-dynamics and a perennial gravitation. 



Let us now look in a wholly different quarter for the mechanical 

 origin of gravitation. In 1870 Prof. Guthrie gave an account of a 

 novel experiment, viz., the attraction of a light body by a tuning- 

 fork when it was set in vibration. Thomson repeated the experiment 

 upon a suspended egg-shell, and attracted it by a simple wave of the 

 hand. Thomson remarks that " what gave the great charm to these 

 investigations, for Mr. Guthrie himself, and no doubt also for many 

 of those who heard his expositions and saw his experiments, was, that 

 the results belong to a class of phenomena to which we may hopefully 

 look for discovering the mechanism of magnetic force, and possibly 

 also the mechanism by which the forces of electricity and gravity are 

 transmitted." By a delicate mathematical analysis, Thomson arrives 

 at the theorem that the " average pressure at any point of an incom- 



