The theory of Mr. Mallet, F.R.S., contained in his now celebrated paper which was read before the Royal Society in 1872, has already been much discussed; but there seems to be still room for the following remarks, which I hope I shall not be thought presumptuous in laying before you.
The treatise is of such considerable dimensions that the simplest plan will be to take the sections of it in order as they occur, passing over those which approve themselves, and discussing only those which appear to be open to question.
There is nothing contained in the first eleven sections but what entirely commends itself to my judgment. Indeed some of the remarks of the distinguished author were anticipated in a paper of mine read at Cambridge in 1868, of which Mr. Mallet had no knowledge at the time when his theory was given to the world.
In § 12 the opinion that the crust of the earth rests on a liquid nucleus is mentioned, but not with favour. Whatever its condition may be at a very great depth, the view which at present seems probable to me is, that there is, at any rate, a substratum in a state of igneous fusion beneath the crust.
In § 15 Mr. Hopkins’s investigation upon precession, according to which he believed himself to have shown that the crust of the earth is at present from 800 to 1000 miles thick, is referred to, but not with approval.
General Barnard, of the United-States