ELECTRICITY IN THUNDER-STORMS.
The circumstances under which electricity was produced were the next subjects of his inquiry, and he says (section 2084):
"The issue of steam alone was not sufficient to evolve electricity. Attaching appendages to the globe, with no water in it, after a few moments and when the apparatus became hot, the issuing steam excited no electricity; but when the steam-globe was filled up with water so far that the rest of the condensed water was swept forward with the steam, abundance of electricity appeared. If then the globe was emptied of its water, the electricity ceased; but, on filling it up again to the proper height, it immediately reappeared in full force. So when the feeder-apparatus was used, while there was no water in the passage, there was no electricity; but, on letting in water from the feeder, electricity was immediately evolved."
It thus appears that, without water to condense the steam, there was no electricity, but with condensation an abundance appeared. Other experiments were to the same effect.
Faraday further says (section 2089):
"If there be no water in the steam-globe upon opening the steam-cock, the first effect is very striking: a good excitement of electricity takes place, but it very soon ceases. This is due to the water condensed in the cold passages producing excitement by rubbing against them. Thus, if the passage be a stopcock, while cold it excites electricity with what is supposed to be steam only; but as soon as it is hot the electricity ceases to be evolved; if then, while the steam is issuing, the cock be cooled by an insulated jet of water, it resumes its power. If, on the other hand, it be made hot by a spirit-lamp before the steam be let on, then there is no first effect. On this principle I have made an exciting passage by surrounding one part of the exit-tube with a little cistern, and putting spirits of wine or water into it."
Experiments with air were also made. It was compressed within a receiver and allowed to escape, impinging against ice or cones of wood or brass (section 2129). With common undried air electricity was produced.
"This I attributed to the particles of water suddenly condensed from the expanding and cooled air rubbing against the metal or wood. Such particles were very visible in the mist that appeared, and also by their effect of moistening the surface of the wood and metal. . . . I proceeded to experiment with dry air (artificially dried by absorbents), and found that it was in all cases quite incapable of exciting electricity against wood or sulphur or brass in the form of cones; yet if in the midst of these experiments I let out a portion of air immediately after its compression, allowing it no time to dry, then it rendered the rubbed wood or brass negative. This is to me a satisfactory proof that in the former case the effect was due to the condensed water, and that neither air alone nor steam alone can excite these bodies, wood, brass, etc., so as to produce the effect now under investigation."
Under all circumstances, then, condensation produced electricity. Without it there was none. The theory of friction is wholly unnecessary to the explanation of the phenomena. It has to assume that water,