PLANETARY EVOLUTION 



will have eaten up all the immense momentum 

 of the planet. A Hindu, wishing to give ex- 

 pression to his idea of the duration of hell-fire, 

 said that if a gauze veil were to be brushed 

 against the Himalaya mountains once in a hun- 

 dred million centuries, the time required for 

 thus wearing away the whole rocky range would 

 measure the tormenfs of the wicked. One mar- 

 vels at such a grandiose imagination ; but the 

 realities of science beggar all such attempts at 

 giving tangible shape to infinitude. The re- 

 sistance of an ethereal medium may work its 

 effects even more slowly than the Hindu's veil, 

 yet in time the effects must surely be wrought. 

 Either the planets are moving in an absolute 

 vacuum — a supposition which is incompatible 

 with the transmission of heat and light — or 

 else the resistance of the medium must tend to 

 diminish their angular velocities. 1 



In the absence of any counteracting agencies 

 — and, after the cessation of the process above 

 described, none such are assignable — this loss 

 of tangential momentum must ultimately bring 

 all the planets into the sun, one after another, 

 beginning with Mercury and ending with Nep- 

 tune. Here the concentration of matter appears 

 to have reached its limit. But what must now 

 happen ? 



1 See Balfour Stewart, in The Conservation of Energy, 

 p. 96. 



307 



