690 THE POPULAR SCIENCE MONTHLY. 



deposition of rain. To this there is no exception. There is, indeed, a 

 manifest relation between the two. The more sudden and rapid the 

 condensation, the more violent and terrific the explosion. 



Sometimes, in thunder-storms we hear a loud crash, and then, soon 

 after, comes an increased pouring down of water. Sound travels more 

 rapidly than rain, and, although the report reaches us first, the interval 

 between the events and the distance traveled plainly indicate that the 

 explosion succeeded the condensation ; and we naturally infer that it 

 was caused by it. The loud crash and simultaneous lightning show the 

 nearness of the explosion, at the origin of the rain-drops. 



I next inquire whether we have experimental proofs corroborating 

 these views. 



A few years since an accidental escape of steam from a steam-boiler 

 was found to strongly electrify a person who stood upon an insulator 

 and held one hand in the escaping steam. This excited much interest 

 at the time, and it was investigated by Armstrong and others, and led 

 to our present steam-boiler electrical machine. The phenomena were 

 at first supposed to throw much light upon the causes of atmospheric 

 electricity. The subject was subsequently taken up by Faraday, who 

 instituted a series of experiments, and came to a different conclusion. 

 His theory, using his own words, was : ' 



" The electricity is due to the friction of the particles of water which the 

 steam carries forward against the surrounding solid matter of the passage, . . . 

 and is in its nature like any other ordinary case of excitement by friction." 



Again (section 2145), he says : 



" Finally, I may say that the cause of the evolution of electricity by the lib- 

 eration of confined steam is not evaporation ; and, further, being I believe fric- 

 tion, it bas no effect in producing and is not connected with the general electricity 

 of the atmosphere." 



The great authority of Faraday has made this, ever since, to be the 

 generally-accepted explanation of the phenomena. It may seem pre- 

 sumptuous to question it, but I cannot think that a careful examination 

 of his experiments will justify all of his conclusions. 



Faraday's apparatus consisted of a small steam-boiler, which he in- 

 sulated, and for the discharge of steam he attached a pipe about four 

 feet long, terminating in an iron globe. This had an orifice to which 

 other appendages could be attached, and there was also a device for 

 injecting water into the exit-pipe. His first experiments were directed 

 to evaporation. He found that when the steam was at full pressure, 

 and the valve was suddenly raised and taken out, and the evaporation 

 was very rapid, no electricity was produced. He charged the boiler 

 with electricity by an electrical machine before the valve was raised, 

 and found that the escape of steam did not affect the charge. It was 

 hence inferred that no electricity was produced by evaporation. 

 1 "Researches in Electricity," vol. ii., section 2085. 



