RECENT PROGRESS IN PHYSICS, 363 



small degree, Faraday conclnded that a solution of ammonia, in the 

 place of pure water, introduced into the escape tube, would still per- 

 mit the development of electricity. Experiment verified this pre- 

 diction. 



The metals, wood, glass, shellac, sulphur, &c., become negative by 

 the friction of the jet of steam and water, while the jet itself is posi- 

 tive. 



An ivory tube, used as an issue piece, causes scarcely any electrical 

 excitement, so that neither the boiler nor the jet is electrified. 



When the neutral jet of steam and water is caused to impinge upon 

 various substances, electricity is developed. If threads or strings of 

 different kinds be stretched upon a fork of stout wire, and then ex- 

 posed, when insulated, to the neutral jet, they become excited, as may 

 be shown by the gold leaf electrometer. In tliis way, Faraday found 

 that linen, cotton, silk, wool, yarn, &c., became negative by the 

 friction of the unexcited jet. 



When Faraday held an insulated wire in the jet, made positive by 

 issuing from a glass or metal tube, at the distance of half an inch 

 from the mouth of the tube, it was not excited ; held nearer to the 

 opening it became negative ; removed to a greater distance, however, 

 it was positive. The reason of this is, that the wire, when near the 

 tube in the forcible part of the current, is excited and becomes nega- 

 tive, rendering the jet more positive than before ; removed further 

 off", in the quieter part of the current, there is no sensible excitement 

 by friction, and the wire then acts only as a conductor to the positive 

 jet, and shows the same state with it. 



If some oil of turpentine be introduced through the stop-copk 

 (fig. 2) into the escape tube, the boiler becomes positive, and the jet 

 negative ; if the stop-cock be closed again, the condition of things 

 is soon reversed, as the oil is very rapidly dissipated. With olive oil, 

 the phenomena are in general the same, — i. e., the jet of stream and 

 water becomes negative, the boiler positive ; but this condition is more 

 permanent, the oil not being volatile. A very little olive oil in the 

 exit tube makes the boiler positive for a long time. 



If a wooden tube be used as an exciter, and some olive oil applied to 

 its inner end, or that at which the steam enters, the boiler becomes 

 positive, and the issuing steam negative ; but if the oil be applied to 

 the outer end of the tube, the boiler becomes negative and the steam 

 jet positive. 



If a simple exit tube be screwed into the steam globe, the oil will 

 produce the same effect as before, provided some oil be put upon the 

 water in the steam globe ; but if the latter contain no|water and only 

 oil, there will be no development of electricity. 



Lard, spermaceti, beeswax, castor oil, resin dissolved in alcohol, 

 and laurel oil act like olive oil and oil of turpentine. 



Faraday thinks that these effects are to be explained by consider- 

 ing that the sides of the tube are rubbed, not by water, but by oil, 

 eacli globule of water being covered by a very thin film of oil. 



In confirmation of this view, that the oil spreads in thin films upon 

 the surface of the water, he has shown that the addition of acid or 

 salt, which in other cases prevents any excitement of electricity, in 



