Penny Blood: Serial Sensation and Working-Class Entertainment — page 75: what you’re looking at

Machine-transcribed from the original scan — historical spelling and the odd misread are preserved.

538 ELEVATIONS ON .THE [cH. v1. of the interior of the earth we have a means, by comparing our result with that already approximately obtained in the case of nature, of judging whether our supposition bears the test of the comparison ; it being always premised that lateral compression 1s the cause of the existence of these elevations; because it is upon this premise that our definition of a datum level, and calculation of 2ke, have been based. Nevertheless our estimate of the average height of the elevations above the profound depths of the sea would hold good as the expression of a fact apart from all theory. In the second chapter it was shown that there is very little question but that the earth was at one time fluid, yet that at the present time we are compelled to admit that it is on the whole rigid: but that it is still open to question whether it is rigid throughout, or whether there is a certain level couche beneath the cooled crust where the pressure is not sufficiently great to induce solidity in rocks which, on account of the increase of temperature in descending, will otherwise be liquid. We have also pointed out how the true law of increase of temperature is inextricably mixed up with the question of the solidity or otherwise of the interior. And if the law of increase of temperature be so, it is evident that the law of cooling, upon which it depends, is also mixed up with the question of the condition of the interior; and the contraction depends on the law of cooling, and the compression on the contraction; so that all these questions are interdependent. Now the laws of cooling of a solid by conduction have been long brought under the dominion of mathematical calculation. Not so those of the cooling of a liquid by convection. Sir Wm. Thomson having satisfied himself that the earth is as @ whole extremely rigid, has assumed that it 1s wholly rigid from centre to surface, and has applied to it the laws of cooling of a solid by conduction. Consequently he has paved the way for an investigation of the amount of compression, which might accrue upon the supposition that the earth has cooled as a solid sphere. To calculate the average height of the elevations, which would have been formed up to the present time under these conditions, is the object of the present chapter. commiclsoolkks (CO) inn ° oe -