THE STORY OF NINETEENTH-CENTURY SCIENCE 



The theory of Le Sage assumes that the entire uni- 

 verse is filled with infinitely minute particles flying in 

 right lines in every direction with inconceivable rapidity. 

 Every mass of tangible matter in the universe is inces- 

 santly bombarded by these particles, but any two non- 

 contiguous masses (whether separated by an infinitesi- 

 mal space or by the limits of the universe) are mutually 

 shielded by one another from a certain number of the 

 particles, and thus impelled towards one another by the 

 excess of bombardment on their opposite sides. What 

 applies to two masses applies also, of course, to any 

 number of masses in short, to all the matter in the 

 universe. To make the hypothesis workable, so to say, 

 it is necessary to assume that the k ' ultra-mundane " par- 

 ticles are possessed of absolute elasticity, so that they 

 rebound from one another on collision without loss of 

 speed. It is also necessary to assume that all tangible 

 matter has to an almost unthinkable degree a sieve-like 

 texture, so that the vast proportion of the coercive par- 

 ticles pass entirely through the body of any mass they 

 encounter a star or world, for example without really 

 touching any part of its actual substance. This assump- 

 tion is necessary because gravitation takes no account 

 of mere corporeal bulk, but only of mass or ultimate 

 solidarity. Thus a very bulky object may be so loosely 

 meshed that it retards relatively few of the corpuscles, 

 and hence gravitates with relative feebleness or, to 

 adopt a more familiar mode of expression, is light in 

 weight. 



This is certainly heaping hypotheses together in a 

 reckless way, and it is perhaps not surprising that Le 

 Sage's conception did not at first arouse any very great 

 amount of interest. It was put forward about a century 



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