342 BELL SYSTEM TECHNICAL JOURNAL 



tell the answer. The antagonist is motion — or, to speak more precisely, 

 momentum — or, to speak yet more precisely, angular momentum. If two 

 particles attract one another but are moving with a relative motion which is 

 not along the line that joins them, they never will meet. However great 

 the attraction between them, it cannot draw them together. Attraction 

 can do no more than constrain them to swing in permanent orbits around 

 their common centre of mass. Therefore, 



The celestial bodies exhibit to us a system kept stable by the attraction of 

 gravity, with motion for the antagonist thereto. 



However natural this statement may now seem, it is by no means an 

 idea inborn in the human mind. There was an era when it was believed 

 that motion dies out of itself, unless continually sustained by a never-ceasing 

 stimulus. Were motion to die out of itself, it could not be an eternal 

 antagonist to gravity. Newton cleared the way for the new idea by abolish- 

 ing the old one. 



May we now assume that the ultimate particles of the world act on each 

 other by gravity alone, with motion as the sole antagonist to keep the 

 universe from gathering into a single clump? 



The answer to this question is a forthright and irrevocable NO. 



That the answer should be no is not at all surprising to this generation, 

 which is familiar with other forces than gravity, the electromagnetic forces 

 especially. Those who underrate the prowess of our forerunners may feel 

 surprise on hearing that the negative answer was quite as apparent to 

 Newton. No apology is ever needed for quoting verbatim what Newton 

 wrote in English, though it is a dangerous act for the quoter, whose writing 

 must suffer by contrast with the simple elegance of the seventeenth century. 

 Incurring the danger, I cite from the Opticks (a book of which the name falls 

 decidedly short of the scope) : 



"The attractions of gravity, magnetism and electricity reach to very 

 sensible distances, and so have been observed by vulgar eyes, and there 

 may be others which reach to so small distances as hitherto escape observa- 

 tion. . . . The parts of all homogeneal hard bodies which fully touch one 

 another stick together very strongly. And for explaining how this may be, 

 some have invented hooked atoms, which is begging the question; and others 

 tell us that bodies are glued together by rest, that is, by an occult quality, 

 or rather by nothing; and others, that they stick together by conspiring 

 motions, that is, by relative rest among themselves . I had rather infer 

 from their cohesion, that their particles attract one another by some force, 

 which in immediate contact is exceedingly strong, at small distances per- 



^ These remarks seem to be aimed at Lucretius, or else at the Greeks from whom 

 Lucretius took some of his ideas. 



