682 THE POPULAR SCIENCE MONTHLY. 



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 Metiers 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 Pois- 

 son, 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 diame- 

 ter offer more resistance than those which are of the same composition 

 and of larger size. The electrical state was conceived in these inves- 

 tigations 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 atmos- 

 phere. 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 accom- 

 modation, when several conductors of unequal power are open to its 

 transmission. A storm-cloud, hovering above in the air, attracts to- 

 ward the nearer part of the terrestrial surface an electrical matter of a 

 contrary nature to its own, and drives back into the ground an electri- 

 cal 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 pro- 

 tected 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 



