There is in Professor Crookes's "Genesis of the Elements" an hypothesis of great interest,--a projectment of philosophical truth which brings him nearer than any known living scientist to the ground held by Keely. Davy defines hypothesis as the scaffolding of science, useful to build up true knowledge, but capable of being put up or taken down at pleasure, without injuring the edifice of philosophy. When we find men in different parts of the world constructing the same kind of scaffolding, we may feel fairly sure that they have an edifice to build. The scaffolding may prove to be insecure, but it can be flung away and another constructed. It is the edifice that is all-important,--the philosophy not the hypotheses. The science of learning, says Professor Lesley, and the science of knowledge are not quite identical; and learning has too often, in the case of individuals, overwhelmed and smothered to death knowledge. It is a familiar fact that great discoveries come at long intervals, brought by specially-commissioned and highly-endowed messengers; while a perpetual procession of humble servants of nature arrive with gifts of lesser moment, but equally genuine, curious, and interesting novelties. From what unknown land does all this wealth of information come? Who are these bearers of it? And who intrusted each with his particular burden, which he carries aloft as if it deserved exclusive admiration? Why do those who bring the best things walk so seriously and modestly along as if they were in the performance of a sacred duty, for which they scarcely esteem themselves worthy? The Bishop of Carlisle, in his paper on "The Uniformity of Nature," suggests the answer to all who are prepared to approach the abyss which has hitherto divided physical science from spiritual science,--an abyss which is soon to be illumined by the sunlight of demonstration and spanned by the bridge of knowledge. To quote from the paper of the Bishop of Carlisle, "There are matters of the highest moment which manifestly do lie outside the domain of physical science. The possibility of the continuance of human existence in a spiritual form after the termination of physical life is, beyond contradiction, one of the grandest and most momentous of possibilities, but in the nature of things it lies outside physics. Yet there is nothing absolutely absurd, nothing which contradicts any human instinct, in the supposition of such possibility; consequently, the student of physical science, even if he cannot find time or inclination to look into such matters himself, may well have patience with those who can. And he may easily afford to be generous: the field of physical science is grand enough for any ambition, and there is room enough in the wide world both for physical and for psychical research."