RESISTING MEDIUM. 205 



certain original arrangements these destructive 

 oscillations are prevented. So long as the bodies 

 continue to revolve, their orbits will not be much 

 different from what they now are. And this re- 

 sult is not affected by the action of the resisting 

 medium. Such a medium cannot increase the 

 small excentricities of the orbits. The range of 

 the periodical oscillations of heat and cold will 

 not be extended by the mechanical effect of the 

 medium, nor would be, even if its density were 

 incomparably greater than it is. The resisting 

 medium therefore does not at all counteract that 

 which is most important in the provision for the 

 permanency of the solar system. If the stability 

 of the system had not been secured by the 

 adjustments which we described in a former 

 chapter, the course of the seasons might have 

 been disturbed to an injurious or even destructive 

 extent in the course of a few centuries, or even 

 within the limits of one generation ; by the effect 

 of the resisting medium, the order of nature 

 remains unchanged for a period, compared with 

 which the known duration of the human race is 

 insignificant. 



But, it may be objected, the effect of the 

 medium must be ultimately to affect the duration 

 of the earth's revolution round the sun, and thus 

 to derange those adaptations which depend on 

 the length of the year. And, without question, 

 if we permit ourselves to look forwards to that 

 inconceivably distant period at which the effect 



