demonstrated that light and electricity differ from each other only as short waves differ from long ones; presumably the same medium serving as the vehicle for both. His masterly experiments thus disclosed another bridge between modes of motion which less than a century ago were accounted distinct and unconnected.
While the establishment of the truth of the conservation of energy justly ranks among the grandest achievements of human thought, that truth would be rounded into satisfying completeness were it proved that energy in all its forms is motion and nothing else. The obstacle here, is that gravity does not lend itself to any kinetic theory thus far framed. And this notwithstanding that atomic weight is the fundamental characteristic of matter, so that, indeed, it conditions every property of a substance—proof of which arrived in the fulfillment of the predictions of Mendelejeef, who, taking this theory as his finder-thought, foretold that scandium, gallium, and germanium would be added to the list of chemical elements, and would be found to possess properties which he detailed. Gravity is marked off from other phases of energy by two characteristics—if it be transmitted through space as are other modes of motion, it either travels instantaneously, or so fast as to elude the observation of astronomers competent to detect its movement were it fifty million times as swift as light. Quite as remarkable is the fact that a mass may be heated, electrified, magnetized, or chemically transformed without its weight being affected in the slightest degree. This in striking contrast with the action of heat, which modifies the color, chemical activity, conductivity, and other properties of a substance, and its volume as well. The only analogy which gravity bears to other forms of energy is that which it sustains to electricity and magnetism, and were these forces attractive only, the analogy would be a close one. But let us trace what analogy there is and we may find it helpful. In the manufacture of a common steel magnet the palpable motion of a dynamo disappears to create its attraction; the imparted dynamo motion therefore is imagined as continuing in full actuality in the molecules of the magnet. When an armature is brought within the magnet's field it is attracted—that is, it powerfully tends to move toward the magnet; until that impulse is satisfied a space divides armature and magnet. All the analogies of light and electricity, proved to be fundamentally one with magnetism, bid us believe that between magnet and armature a medium is actively concerned in bringing both masses together; why may not a similar, or that identical, medium be active in bringing from a tree an apple to the earth? What is needed here is investigation of how the motion of a molecule in its own orbit, or on its axis, becomes
