In the article in _Nature_, from which we have already quoted, Mr. David Forbes mentions that M. De Launay, Director of the Observatory at Paris, 'an authority equally eminent as a mathematician and an astronomer,' having carefully considered Mr. Hopkins's problem, decided that its data were incorrect, and that it could shed no light whatever on the question whether the globe is liquid or solid. There is some doubt, however, as to the import of M. De Launay's statement. We may be the more disposed to wonder at the decision with which Sir Charles Lyell pronounces upon this subject in his latest edition, by the fact that, since the publication of the previous edition, he has modified, to a very serious extent, his conception of the evidence on which the theory which he adopts is based. In the ninth edition of the 'Principles' he laid so much stress on Sir Humphry Davy's hypothesis of an un-oxidized metallic nucleus of the globe, liable to be oxidized at any point of its periphery by the percolation of water, and thus to evolve heat sufficient to melt the adjacent rocks, that Hugh Miller, in contending against Sir Charles, selected this as an essential part of the argument. In his tenth edition Sir Charles does not even mention Sir Humphry Davy's theory. The star under the influence of which the tenth edition was prepared was that of Mr. Darwin. No brighter star may be above the geological horizon, and Sir Charles may have done well to own its influence, but we submit that opinions which undergo important modification within a few years ought hardly to be promulgated as marking the limit between the era of darkness and the era of light in geological discovery.