294 ANNUAL OP SCIENTIFIC DISCOVERY. 



the globe, to one in which the local distribution of heat was more marked 

 and the climate more " excessive," the mean temperature of the polar regions 

 becoming certainly less, and possibly that of the equatorial regions rather 

 greater, than before. It is obvious that such a change is one that cannot be 

 accounted for by any shifting of the earth's axis. 



But even if we dismiss palseontological arguments, and look solely to the 

 form of the earth, it seems to me that we have good reason to doubt the pos- 

 sibility of a change in the earth's axis of rotation. Admitting the assump- 

 tion adopted by Sir Henry, that the earth was at first a fluid mass, and 

 afterwards a mass with a hardened crust, it follows that, if it rotated with 

 the same velocity as now, the oblateness of its spheroid must have been 

 originally as great as it is now. That oblateness may be conceived thus : If 

 we imagine a perfect sphere to be described about the centre of the earth, with 

 the distance from the centre to the poles as its radius, the surface of that 

 sphere would coincide with the earth's surface about the poles, but would 

 sink regularly as we receded from them, until it reached a depth of about 

 thirteen and a quarter miles at the equator. The earth must have had then, 

 ab initio, a protuberant shell, gradually bulging beyond the form of a true 

 sphere, till it reached to the extent of thirteen and a quarter miles, or nearly 

 seventy thousand feet, about its equator. It is very difficult to see what 

 force, internal or external, could have given to a globe thus weighted and 

 balanced all round such a permanent lilt as would cause it to spin on any 

 other than its shortest diameter, or could so alter its form as to make any 

 other diameter shorter than its original axis of rotation. The highest moun- 

 tain in the world, Mount Everest, is only five and a half miles high, one- 

 third of that height being a mere pinnacle. The table-laud of Thibet, with 

 the Kouenlun and Himalaya mountains, is certainly the largest projecting 

 mass above the surface of the earth ; but^ its mean height cannot be ureater 

 than two and a half miles, and its greatest diameter is only some six or 

 seven hundred miles. Ls mass, therefore, can bear but a very small propor- 

 tion to the mass of the protuberant belt surrounding the earth in its latitude, 

 and still less to the whole protuberant shell, and can, therefore, have but an 

 equally slight influence in overcoming the effect of that shell in giving equi- 

 librium to the earth's motion. If the much greater irregularities in the 

 earth's surface, namely, those prominences which form the masses of dry 

 land, and those hollows in which the ocean lies, be wholly within the pro- 

 tuberant shell of the earth, and I think that we can have no doubt that 

 they are so, except in the immediate neighborhood of the poles, and if 

 these great irregularities balance each other, and the equilibrium of the earth 

 be maintained, it appears to me that the addition or subtraction of a mere 

 wrinkle such as the Alps, the Andes, or the Himalayas, could hardly have 

 more than an infinitesimal effect on that equilibrium. But the nearer the 

 irregularities are to the pole, the less would be their disturbing effect, so that 

 high land or deep sea there (and the Arctic Sea, at all events, seems compar- 

 atively shallow) would have less effect than in lower latitudes, while exactly 

 as the latitude decreases the compensating protuberance increases. 



Sir Henry assumes that our present mountain chains were once much 

 greater than they are now, because such vast masses of rock have been 

 removed from above those of which the present mountains are composed. 

 I fully agree with him in the vast amount of erosion and denudation that 

 has taken place over all our mountain chains; but, then, I believe that ero- 

 sion was caused by the wearing action of the sea as the mountains slowly 



