_Sir William R. Grove on the pre-nebular condition of matter._—Amongst the first to advocate the view that ordinary matter is everywhere present in space was Sir William R. Grove. In a lecture delivered at the London Institution as far back as January 1842, he stated that it appeared to him that heat and light, according to the undulatory theory, were the result of the vibrations of ordinary matter itself, and not that of a distinct ethereal fluid. Twenty years afterwards, referring to the views he then advanced, he says: “Although this theory has been considered defective by a philosopher of high repute, I cannot see the force of the arguments by which it has been assailed; and, therefore, for the present, though with diffidence, I still adhere to it.”[64] [Footnote 64: _Correlation of Physical Forces_, p. 164 (fifth edition), 1867.] He adduces a great many facts and forcible arguments in support of his position. He says that “there appears no reason why the atmosphere of the different planets should not be, with reference to each other, in a state of equilibrium. Ether, or the highly attenuated matter existing in the interplanetary space, being an expansion of some or all of these atmospheres, or of the more volatile portions of them, would thus furnish matter for the transmission of the modes of motion which we call light, heat, &c.” It is assumed in the theory, of course, that matter must form a universal planum. Sir William Grove favours the idea that the universe is illimitable in extent, a view held by many eminent thinkers. EVOLUTION OF THE CHEMICAL ELEMENTS, AND ITS RELATIONS TO STELLAR EVOLUTION.