Page:Popular Science Monthly Volume 25.djvu/698

682 distinguished meteorologist who first ascended four miles and a half into the air in a balloon. The second and the third were prepared in 1854, and in 1867, by M. Pouillet, the director of the Conservatoire des Arts et Métiers in Paris, and the author of a well-known work on the elements of experimental physics and meteorology, which has been translated into many languages. These reports, although drawn up by an individual, were the results of the deliberations and experiments of a considerable number of scientific men, acting as a commission, and comprising among them such distinguished names as those of Poisson, Fresnel, Becquerel, Duhamel, Fizeau, and Regnault. In the first of these reports, that, namely, of Gay-Lussac, which was adopted by the Academy of Sciences on April 23, 1823, it was premised as a kind of axiom that there are no bodies which do not offer some resistance to the transmission of electricity, and that conductors of small diameter offer more resistance than those which are of the same composition and of larger size. The electrical state was conceived in these investigations as consisting of some kind of matter—as depending upon molecules which are mutually repulsive, and which therefore tend to separate and disperse themselves through space, and which are only retained upon the surface of solid bodies by the pressure of the atmosphere. When the electric matter escapes, it seeks the earth under its tendency to diffuse itself over the most capacious conductors it can find, selecting the most perfect of them that are within its reach, but dividing itself in proportion to their individual capacities of accommodation, when several conductors of unequal power are open to its transmission. A storm-cloud, hovering above in the air, attracts toward the nearer part of the terrestrial surface an electrical matter of a contrary nature to its own, and drives back into the ground an electrical matter of the same nature as its own. Each prominent part of the ground is therefore, for the time, in a state of electrical tension during the presence of a neighboring storm-cloud, and becomes a center of attraction toward which the lightning inclines. When the prominent object is in good connection with the ground, its electrical matter may shoot forth toward that of the cloud, and make a path between it and the cloud. If the prominent body projects as a sharp point toward the cloud, the escape of the electric matter from it to the cloud becomes very rapid, and the lightning strikes to it from the cloud, from a greater distance. It was further conceived that a good conductor protected from any violent discharge a circular space whose radius was twice the height of the rod. An iron bar three quarters of an inch square was taken to be of sufficient dimensions for the construction of a conductor, because no instance had been known of a rod a little in excess of half an inch in diameter having ever been fused or raised to a red heat by lightning. Even small rods or wires that were dispersed by the passage of lightning had served to convey it to the ground, and had protected surrounding objects from single strokes. Trees were