448 THE MULTIPLICATION OF EFFECTS. 



Here then is a secondary series of effects : far more numerous 

 though far smaller in their amounts. As these indirect per- 

 turbations must to some extent modify the movements of 

 each planet, there results from them a tertiary series; and 

 so on continually. Thus the force exercised by any planet 

 works a different effect on each of the rest; this different 

 effect is from each as a centre partially broken up into 

 minor different effects on the rest; and so on in ever multi- 

 plying and diminishing waves throughout the entire system. 



§ 158. If the Earth was formed by the concentration of 

 diffused matter, it must at first have been incandescent ; and 

 whether the nebular hypothesis be accepted or not, this orig- 

 inal incandescence of the Earth must now be regarded as in- 

 ductively established — or, if not established, at least ren- 

 dered so probable that it is a generally admitted geological 

 doctrine. Several results of the gradual cooling of the 

 Earth — as the formation of a crust, the solidification of sub- 

 limed elements, the precipitation of water, &c, have been 

 already noticed — and I here again refer to them merely to 

 point out that they are simultaneous effects of the one cause, 

 diminishing heat. Let us now, however, observe the multi- 

 plied changes afterwards arising from the continuance of 

 this one cause. The Earth, falling in temperature, 



must contract. Hence the solid crust at any time existing, 

 is presently too large for the shrinking nucleus; and being 

 unable to support itself, inevitably follows the nucleus. But 

 a spheroid envelope cannot sink down into contact with a 

 smaller internal spheroid, without disruption: it will run 

 into wrinkles, as the rind of an apple does when the bulk 

 of its interior decreases from evaporation. As the cooling 

 progresses and. the envelope thickens, the ridges conse- 

 quent on these contractions must become greater; rising 

 ultimately into hills and mountains; and the later systems 

 of mountains thus produced must not only be higher, as we 

 find them to be, but they must be longer, as we also find 



