LIGHTNING (ante). The abbe Nolet is said to have been the first to remark the similarity of phenomena in discharges of lightning and of the electrical machine, but there was no experimental determination of the identity of their nature until Benjamin Franklin made his celebrated investigation of the subject by the use of a kite at Phila delphia in 1752. Three years previous to this, however, he made some interesting remarks upon the subject in his Observations on Electricity, showing that his mind had comprehended the causes even before he made his demonstrative experiments. He says: " Where there is a great heat on the land in a particular region the lower air is rarefied and rises; the cooler, denser air above it descends; the clouds in the air meet from all sides and join over the heated place; and if some are electrified, others not, lightning and thunder succeed and showers fall. Hence, thunder gusts after heats, and cool air after gusts. As electrical clouds pass over a country, high hills, trees, toweu, chimneys, etc., draw the electric fire, and it is therefore dangerOus to take shelter under a tree dur ing a thunder gust. It is safer to be in the open fields for another reason. When the clothes are wet, if a flash, iu its way to the ground, should strike yourhead it may run in the water over the surface of your body, whereas if your clothes were dry it would go through the body." Again: " Now, if the fire of electricity and that of lightning be the same, as I have endeavored to show in a former paper, and a tube of only- 10 ft. long will discharge its fire at 2 or 3 in. distance, an electrified cloud of perhaps 10,000 acres may strike and discharge on the earth at a proportioually greater distance." Speaking of the discharging power of points he says: "May not a knowledge of this power of points be of use to mankind in preserving houses, churches, ships, etc., from the stroke of lightning by directing us to fix, on the highest parts of those edifices, upright rods of iron made sharp as a needle, and gilt to prevent rusting, and from the foot of the rods a wire down the outside of the building into the ground, or down round one of the shrouds of a ship, and down her sides till it reaches the water? Would not the pointed rods probably draw the electric fire silently out of the cloud before it came near enough to strike, and thereby secure us from the most sudden and terrible mischief?" He pro posed various experiments, and, acting under his instructions, Dalibard had drawn electric sparks from an iron rod 40 ft. high at Marly in France, and had chargecl.Leyden jars with the apparatus, May 10, 1752. Franklin did not make his kite-experiment till more than a month later, viz., June 15. It was natural that these experiments should be repeated all over the civilized world. Prof. Richman of St. Petersburg was killed, in the sumtner of 1753, by a bolt of lightning in die form of a blue ball as large as a man's fist which leaped from the insulated conductor to his head, which was about a foot distant. His companion was struck senseless and a door was torn from its place by the stroke. In the experiment of 31. Romas of .Nerac, France (see ante). which has been said by some to antedate Franklin's, he used a kite of about 18 sq.ft. surface, with v, copper wire wound around the string, and an insulating silk cord at the ground end, near which an iron tube was placed as a secondary conductor. When the kite was at a height of 550 ft. during a storm, flashes of fire darted to the earth attended by loud
explosions, and all light bodies in the vicinity were alternately, positively and negatively, electrified and propelled in various directions.
It has been shown by Cavallo, De Saussure, and others that the electrical condition of the atmosphere, in comparison with that of the earth, is positive; also, by La place, Lavoisier, Volta, and De Saussure that the cause of atmospheric electricity is evaporation from the surface of the earth; but, according to the experiments of PouiIlet, evaporation does not produce opposite electrical conditions unless accompanied by chemical decomposition or separation of vapor front saline solutions, or from oxidizing surfaces or the leaves of growing plants. Currents of wind rushing over opposing objects, occasioning disturbance of electric equilibrium, are among the chief causes of atmospheric electricity, the electricity passing with the wind to elevated regions; or, on the two-fluid hypothesis, positive electricity being carried upwards, while the negative passes to the earth. In regard to the production of the various kinds of lightning and thunder, they may be explained according to a variety of circumstances. To account for the variations in tone and intensity of a thunder-clap as heard at a certain point— that is to say, to explain what conditions were present and what form or dimensions the discharge had—would be very difficult, perhaps impossible, from the fact that it is impossible to appreciate the extent of the process and the direction of the discharge or discharges. The reverberation of sound may be the result of one discharge, Which is echoed from peak to peak or from crag to crag and probably from cloud to cloud, although the power of clouds to reflect sounds has not been determined. There may he a succession of discharges from different portions of different clouds .to those of others,, one explosion being succeeded by another in consequence of changes of electrical con.
ditions in various parts of the celestial and terrestrial apparatus. The increased intensity of a roll of thunder is probably to be accounted for in this way. The first sounds may be produced by successive minor discharges, causing electrical conditions between two, larre masses of clouds, or between a large mass and the earth, which result in the exchange of Farge quantities of electric fluid, or the descent of a powerful bolt to the earth. Although many phenomena of electricity are well known, and the electricity of chemical batteries can be measured and rendered serviceable, still its real nature is not known. It is not positively determined whether it is an imponderable body, an imponderable force, or merely a phenomenon resulting from the conditions of.the matter with -which it is con: nected. Until its nature be determined it cannot be said whether a ball of lightning is a moving mass of elearical matter, or of other matter in a peculiar electrical state. There is something wonderfully interesting and inexplicable in some of these moving masses. of apparent fire. The ordinary laws of electrical attraction and repulsion will scarcely serve to explain their various freaks. They often seem as if propelled from behind, in the manner of ai) ordinaiy projectile; and the manner in which they pass into dwellinns; and demolish walls may indicate that they are driven against bodies, and not attracteil by them.