182 



ATMOSPHERICAL ELECTRICITY. 



[1854. 



with greater or less violence in tile air, all which probably are 

 concerned in the production of the electricity we observe in it; 

 namely, 1. Evaporation; 2. The friction of the wind; and 3. 

 Combustion. As early as 1749, Franklin had a theory that 

 electricity was produced by evaporation, and in a way which 

 had some resemblance to Black's theory of specific heat. When 

 water evaporates, it requires a greater capacity for electricity as 

 well as for heat. The electricity and heat, essential to the 

 physical change of state involved in the transition of matter 

 from a liquid to a gaseous state, must be abstracted from sur- 

 rounding bodies which are thus cooled and left, electrically 

 speaking, negative. As the vapor rises with its latent charge of 

 heat and positive electricity, it finally reaches a region of cold 

 where it is again condensed, and the electricity and heat be- 

 come free again, and make some demonstration. Thus, if Frank- 

 lin had reasoned by strict analogy, he would have made the 

 charge of the clouds positive, whereas at this time he was under 

 the impression that they were negatively electrified. In 1767, 

 he had come to the opinion that the vapor is often positive. In 

 the mean while, that is, in 1752, Nollet had made experiments 

 upon evaporation. In 1782, Volta published his experiments 

 upon electricity as a product of evaporation ; especially that which 

 he made by a mixture of water, sulphuric acid, and iron filings, 

 in the presence of Laplace and Lavoisier. Saussure andBennet 

 also experimented on the evaporation of various liquids and from 

 various vessels they remark that the kind of electricity developed 

 in . the vapor was often anomalous. Saussure suggested, that 

 in some, cases a chemical decomposition of the liquids might 

 take place, or perhaps even of the vessel, which disguised the 

 genuine result of evaporation. Pouillet, who has gone largely 

 into the subject of the origin of atmospherical electricity, has 

 come to the conclusion, that the material of the vessel which 

 holds the evaporating water has much influence, and that pure 

 distilled water develops no electricity by evaporation; and that 

 the saline or other impurities which water generally contains are 

 in some way essential for the production of electricity by evapo- 

 ration. If, says Bird, common salt be put into the water which 

 is passing into vapor, the vapor acquires positive electricity at 

 the cost of the vessel, which is negative. If, on the other hand, 

 acid is mixed with the water, the vessel takes the positive charge 

 and the vapor goes up with a deficiency of electricity. Peltier 

 has made many experiments upon the subject, and finds, as he 

 thinks, something besides evaporation to be necessary to the pro- 

 duction of electricity, and something the conditions of which can 

 hardly be found in ordinary evaporation. It is proper, also, to 

 add this fact given by Pouillet, that Lemonnier discovered 

 electricity in the air every day for six weeks between the middle 

 of September and the end of October, 1753, although the season 

 was very dry and no clouds were seen. On the other hand to 

 prove that evaporation developed electricity, Rowell and Spencer 

 made an experiment which showed that, where electricity was 

 cut off by insulation, the evaporation was retarded. For this 

 purpose, they put the same weight of water into two vessels, one 

 of which was insulated, and the other connected with the ground 

 by conductors of electricity, and they always found that the latter 

 lost the most by evaporation. I will give the following method of 

 Howard for showing the electricity of evaporation: " To the 

 cap of a gold-leaf electroscope I affixed a horizontal support for 

 a candle, which projected two feet from the cap of the instru- 

 ment placed near the edge of a table; on the floor, immediately 

 beneath, was an earthen vessel containing hot water an inch in 

 depth. The candle being lighted, two or three hot coals were 

 dropped into the water, so that there rose a sudden cloud of 

 vapor. The electricity of this being collected by the candle, the 

 leaves of the electroscope opened and struck against the sides." 



Another cause of atmospherical electricity, and the one upon 

 which Rciss particularly insists, is friction. Faraday shows by ex- 

 periment that dry air,rubbing against dry airor againstsome other 

 substance, would be inactive in respect to electricity. But moist air 

 grinding against the hills, the trees, the rocks, would acquire a 

 positive charge of electricity. The friction of two masses of 

 moist air driven by opposite currents against one another might 

 charge each, though with different kinds of electricity, and to a 

 less degree than where the two rubbing bodies are more hetero- 

 geneous. IOemtz, the distinguished meteorologist, relies on the 

 efficacy of friction, — of friction between strata of air differing in 

 temperature as well as moisture, of which the coldest, and there- 

 fore generally the highest, takes the positive charge. In eluci- 

 dation of this point, I may refer to the discovery by Armstrong, 

 in 1840, or hydro-electricity, as it is called. When high pressure 

 steam issues from a boiler through a stopcock, lined, for example, 

 with partridge-wood, electricity is abundantly produced ; the 

 steam and water being charged positively and the boiler 

 negatively. The elaborate experiments of Faraday have clearly 

 shown that the cause of the electricity in this case is friction ; 

 not the friction of the steam, but of the liquid particles mixed 

 with the steam, against the inside of the pipe. Dry steam will 

 not answer. Hence the apparatus makes provision for cooling 

 and condensing, by a circuitous channel artificially chilled, a part 

 of the steam before it escapes, so that it may contain the particles 

 of water which do the rubbing. The steam itself is the 

 mechanical power which works the electrical engine. The 

 hydro-electric machine accordingly differs from the ordinary 

 friction machine for producing electricity, incidentally in employ- 

 ing steam power instead of manual labor to work it, but 

 essentially in selecting drops of water and wood for rubbing in 

 place of glass and the usual amalgamated rubber. Leave now 

 the workshop and the laboratory and go out into the broad at- 

 mosphere, substitute for the working power of steam that of the 

 wind, and you have a hydro-electric machine of Nature's own 

 handiwork, and upon a magnificent scale. I will offer only two 

 further remarks concerning friction, as one of the contracting 

 parties for forging the glittering artillery of the clouds. 1. As 

 friction of the air is inoperative without moisture, evaporation in 

 the last analysis is to be thanked for the electricity which friction 

 produces. 2. As the friction of moist air, as it is driven before the 

 wind, must be one cause, if not the only or principal cause, of 

 atmospherical electricity, have we not some elucidation of the 

 thunder and lightning which accompanies many moist storms, 

 and makes so dazzling a part of the retinue which marches in the 

 track of the tropical hurricane and the tornado everywhere ! 



Vegetation and combustion must not be omitted in making a 

 catalogue of the sources of atmospherical electricity. Pouillet 

 inferred from experiments, that the oxygen which plants give 

 out by day is charged with negative electricity; and that a 

 surface of one hundred square metres in full vegetation pro- 

 duces as much electricity in one day as the largest Leyden bat- 

 tery can contain. Krerntz lays some stress on combustion as a 

 generator of atmospherical electricity. The carbonic acid gas 

 carries off with it positive electricity. 



This experiment of Matteucci may have some applicability to 

 the subject. He insulated a metallic plate of three square feet, 

 covered with earth and salt; as soon as the sun acted upon it, 

 the gold leaves of an electroscope connected with it diverged. 



After it has been proved that an assigned cause is of the 

 right kind in quality, the demands of a rigid science are not 

 satisfied unless it is also shown that it is of sufficient force in 

 quantity. In the case under consideration, it may be difficult to 



