other, and air or gases charged with similar electricities are equally self-repellent. Professor Tyndall, in his "Lessons in Electricity," says, "The electricity escaping from a point or flame into the air renders the air self-repulsive. The consequence is, that when the hand is placed over a point mounted on the prime conductor of a good machine, a cold blast is distinctly felt.... The blast is called the 'electric wind.' Wilson moved bodies by its action; Faraday caused it to depress the surface of a liquid; Hamilton employed the reaction of the electric wind to make pointed wires rotate. The wind was also found to promote evaporation." While electrical repulsion is doubtless analogous to, and correlative with, the attraction of gravitation, this force, and even gravity itself, has been sometimes interpreted as derived from the mutually interacting molecules of space itself. We may even learn somewhat of how such repulsions of similar and attractions of opposite electrospheres might occur. We constantly speak of positive and negative electricity as though these were different fluids, but such expressions are employed only in the same manner as the analogous terms, heat and cold. We know, of course, that cold is the relative absence of heat, the dividing line being not a fixed, but a constantly changing one, so that one body is cold to another by reason of relative, and not absolute, deprivation of heat. It is well known, however, that cold, which is purely a negative state, manifests the same apparent radiant energy as heat. A vessel near an iceberg is exposed to a wave of cold, precisely as of heat from a heated body at the same distance. This, of course, is due to abstraction and not to increment. All space being occupied by attenuated matter in a state of unstable electrical equilibrium, as we say, which simply means a condition ready to be raised or lowered in tension by absorption from or into outside media, all concrete bodies floating in that space must have an electrical potential either equal to, or higher, or else lower than that of their surrounding space. A solitary body in space, if we can conceive of such, in either a higher or lower state of electrical tension, would be drawn upon from all sides to equalize the distribution and restore the general average. But if two bodies occupy the same field, and are widely different from each other in electrical potential, one higher and the other lower than that of space, this distribution will be towards each other, and must be manifested by mutual attraction. But if, on the contrary, these two bodies are both equally higher or lower than the spatial average, they have nothing to give to each other, but have this difference to give to or receive only from outer space, and hence they will be drawn apart or, as we say, mutually repelled. The case is similar to what we see in the case of bodies of water at various levels. Suppose