by direct outblow of the sun, so to speak, upon the incandescent gases of the tail itself. This fact clearly demonstrates that the repulsion of like electrospheres is the cause of the phenomenon, and, when once understood, the process is quite as simple as that of the original formation of the tail itself, which no one disputes. There is to be further considered the theoretical resistance of space to the projection and deflection of such enormous volumes of attenuated matter as appear in comets' tails. While it may not be absolutely necessary to offer an explanation of this apparent difficulty, in view of the fact that such projection and deflection do actually occur, still, the well-known laws of the diffusion of gases, in accordance with which any gaseous matter will traverse any other gaseous matter with the same velocity as, and with no more resistance than, in a vacuum, will show that this difficulty has been much overrated, while for the twin difficulty, how to account for the persistence of luminosity at such vast distances from its source, we may quote from Professor Proctor, "Cometic Mysteries," who, in turn, quotes as follows: "Comets travel in what must be regarded as to all intents and purposes a vacuum. From Dr. Crookes' experiments on very high vacua we may infer that there is very little loss of heat, except by radiation." By "intents and purposes" we understand, of course, as a cause of resistance, and certainly there is no reason to believe that the attenuated vapors of space are sufficient in density to cause any rapid diffusion of heat by convection, as contrasted with that of radiation. We have seen that comets of short period sometimes disappear, and that their disappearance is frequently followed by the appearance of trains of meteors. In other words, they have apparently lost their cometic properties and become permanent adjuncts to our solar system. A curious confirmation of this fact is to be found in the character of the occluded gases which are contained in such meteorites as sometimes fall upon the earth's surface. Of this Professor Proctor says, "We have reason to believe that the nucleus of a comet consists of an aggregation of stones similar to meteorites." Speaking of the condition in which meteorites reach the earth, he says, "They are known to contain as much as six times their own volume of gases (taken at atmospheric pressure). In one of these meteorites recently examined by Dr. Flight, the following percentages of various gases were noted: Of carbonic oxide, 31.88; of carbonic acid gas, 0.12; of hydrogen, 45.79; of olefiant gas, 4.55; and of nitrogen, 17.66." The presence of olefiant gas at once suggests the hydrocarbons of the cometic nucleus. The presence of this gas cannot be accounted for by the passage of the meteorite through our atmosphere, nor can that of hydrogen, and these are two characteristic gases, together with the vapor of carbon, constantly found to exist in comets.