L'Abbé Nollet, considered in the France of his time as an oracle in regard to natural philosophy, expressed himself as follows upon this subject:--"If some one, after comparing the phenomena, were to undertake to prove that thunder is in the hands of nature what electricity is in ours, that those electrical wonders with which we are now able to make so much play are petty imitations of those great lightning effects which frighten us; that both result from the same mechanism; and if he could make it evident that a cloud produced by the action of the winds, by heat, and by the mingling of exhalations, bears the same relation to a terrestrial object as an electrified body bears to an unelectrified body in its close proximity, I admit that the idea, if well worked out, would captivate me greatly; and, to work it out, how many plausible arguments there are at the disposal of a man who is properly versed in electricity!" The invention of the Leyden jar in 1746, and Franklin's brilliant investigations, make these conjectures the more probable. Since then electricity has gone ahead and become one of the most important branches of modern natural philosophy. When Franklin demonstrated that the air is in a permanent condition of electrification even when the sky is clear, people began to study not thunder alone but the general electrical state of the atmosphere. And ever since meteorological observatories have made it a practice to register every day the degree and nature of atmospheric electricity by the use of very ingenious instruments. But the records obtained up till now leave us in doubt upon many points. The subject is still full of new surprises. Whence come those masses of electricity which move about in the clouds, sometimes escaping from them in thunderclaps and causing such tremendous ravages upon this earth of ours? The evaporation of the sea is one of their principal causes. The atmosphere is continually impregnated with electric effluvia which flow silently through the soil through the medium of all bodies, organized or not, attached to the earth's surface. Plants afford an especially welcome pathway to this fluid. The green leaves you see rustling in the wind are often being traversed by electrical currents, luckily harmless, of precisely the same nature as those of the deadly lightning. On the other hand, the earth itself emits a certain quantity of electricity, and it is from the attraction exerted by these two fluids upon each other that thunder comes into existence. To put it in another way, thunder is a sudden striking of a balance between two different masses of electricity. Minute researches have established the fact that in ordinary conditions the terrestrial globe is charged with resinous, or negative electricity, while the atmosphere holds in suspension _vitrée_, or positive electricity.