UNSETTLED VIEWS OF NEWTON. 39 



any given centre. And it will be proved here- 

 after, that the aether is more dense within the 

 pores and around the particles of dense than of 

 light bodies, in which it is more dense than in 

 free space. On the whole, it is not very sur- 

 prising that Newton's views of the aether have 

 been generally regarded as chimerical, and in- 

 sufficient to explain the leading phenomena of 

 nature ; especially as he never identified it with 

 any known principle. And when he referred 

 the centripetal forces of matter to its agency, he 

 assigned no physical cause of the centrifugal 

 force. But if the centrifugal force of planets be 

 directly in proportion to the radiating power of 

 the solar orb, caloric must be the cause of this 

 force : for the essential character of a vera causa 

 is, that the effects it produces are a measure of 

 its intensity.* 



Nor is it less certain, that if the caloric which 

 is perpetually radiated from the sun be not anni- 



* Moreover, as the mean temperature of the earth has remained 

 the same for long periods of time, it follows that the planets must 

 give off by radiation the same amount of caloric they receive from 

 the sun. This amount must depend on their superficial area, and 

 on their distance from the sun. It therefore becomes an important 

 question, how far it may operate in producing the centrifugal 

 force of their satellites, just as the radiating power of the sun 

 generates the centrifugal force of the planets themselves. At the 

 same time it must be observed, that the motions of the satellites 

 are subject to the direct influence of the sun ; which, however, is 

 greatly diminished by his immense distance, compared to the 

 nearness of their primaries. For as Sir John Herschel observes, 



