Gravitation remains a puzzle to science. The tendency of modern physics is to explain all material phenomena in terms of electrons and the ether, but the attempt to account for gravitation in this way is attended with difficulties. In order to cope with these, it seems necessary to assume that our universe is only a portion of a greater universe. This assumption readily lends itself to the conception of our universe as a three-dimensional meeting place of two portions of a universe of four dimensions--that is, its conception as a "higher" surface. This is a fundamental postulate of higher space speculation. One hypothesis advanced to explain gravitation assumes the existence of a constant hydrostatic pressure transmitted through the ether. A steady flow of ether into every electron in a gravitating system of bodies would give rise to forces of attraction between them, varying inversely as the square of the distance, according to Newton's law. But in order to avoid the conception of the continual destruction and creation of ether, it is necessary to assume a steady flow through every electron between our universe and the greater universe of which it is assumed to form a part Now because the electrons, in order to receive this flow, must lie on the boundary of this greater universe, the latter must be four-dimensional. Every electron, in other words, must be the starting point of a pathway into--and a terminal point out of--four-dimensional space. Here we have another familiar higher space concept. THE ETHER OF SPACE The ether of space, because it has at last found entrance, must be given a grudging hospitality in these pages, even though the mysterious stranger prove but a ghost. The Relativists would have it that with the acceptance of their point of view the ether may be eliminated; but if they take away the ether, they must give us something in its stead. In whatever way the science of the future disposes of this problem, it must take into account the fact of light transmission. On the theory that the ether is an elastic solid of amazing properties, in which the light waves vibrate _transversely_ to their direction, it assists the mind to think of the ether as four-dimensional, because then a light wave would be a superficial disturbance of the medium--superficial, but three-dimensional, as must needs be the case with the surface of a four-dimensional solid. * * * * *