May :51, 1895.] 



SCIENCE. 



591 



centimeters deep. He had been engaged in 

 studying the great negative potential which 

 had been found in air in the neighborhood of 

 waterfalls, and which had generally been 

 attributed to the inductive action of the 

 ordinary fine weather electric force, giving 

 negative electricity to each drop of water- 

 spray before it breaks away from conduct- 

 ing communication with the earth. Before 

 he knew Maclean and Goto's paper, he had 

 found strong reason for believing that that 

 theory was not correct, and that the true 

 explanation of the electrification of the air 

 must be found in some physical action not 

 hitherto discovered. A less thorough in- 

 quirer might have been satisfied with the 

 simple explanation of the electricity of 

 waterfalls naturally suggested bj' Maclean 

 and Goto's result, and might have rested in 

 the belief that it was due to an electrifj-ing 

 effect produced by the rush of the broken 

 water through the air ; but Lenard made an 

 independent experimental investigation in 

 the Physical Laboratories of Heidelberg and 

 Bonn, by which he learned that the seat of 

 the negative electrification of the air electri- 

 fied is the lacerated water at the foot of the 

 fall, or at any rocks against which the water 

 impinges, and not the multitudinous inter- 

 faces between air and water falling freely in 

 in drops tlirough it. 



§ (5. It still seems worthy of searching in- 

 quiry to find electrification of air by water 

 falling in drops through it, even though we 

 now know that if there is anj- such electrifi- 

 cation it is not the main cause of the great 

 negative electrification of air which has been 

 found in the neighborhood of waterfalls. 

 For this purpose an experiment has been 

 verj' recently made by Mr. Maclean, Mr. 

 Gait and myself, in the course of an investi- 

 • gation regarding electrification and diselec- 

 trification of air with which we have been oc- 

 cupied for more than a year. The apparatus 

 which we used is before you. It consists of 

 a quadrant electrometer connected with an 



insulated electric filter* applied to test 

 the electrification of air drawn from differ- 

 ent parts of a tinned ii-on funnel, 187 centi- 

 meters long and 15 centimeters diameter, 

 fixed in a vertical position with its lower 

 end open and its upper end closed, except a 

 glass nozzle, of 1.6 mm. aperture admitting 

 a jet of Glasgow supply water ( from Loch 

 Katrine) shot vertically down along its 

 axis. The electi'ic filter (r in the draw- 

 ing), a simpUfied and improved form of 

 that described in the Proceedings of the 

 Royal Society for March 21, consists of 

 twelve circles of fine wire gauze rammed as 

 close as possible together in the middle of a 

 piece of block tin pipe of 1 cm. bore and 2 cm. 

 length. One end of it is stuck into one end 

 of a perforation through a block of paraffin, 

 K, which supports it. The other end (g) 

 of this perforation is connected by block 

 tin pipe (which in the apparatus actually 

 emploj'ed was 4f meters long, but might 

 have been shorter), and india-rubber tubing 

 through bellows to one or other of two 

 short outlet pipes (m and p) projecting from 

 the large funnel. 



§ 7. We first applied the india-rubber 

 pipe to draw air from the funnel at the 

 upper outlet, p, and made many experi- 

 ments to test the electricity given bj- it to 

 the receiving filter, r, under various condi- 

 tions as to the water-jet ; the bellows being 

 worked as uniformly as the operator could. 

 "When the water fell fairly through the fun- 

 nel with no drops striking it, and through 

 yO cm. of free air below its mouth, a small 

 negative electrification of r was in every 

 case observed (which we thought might 

 possibly be attributable to electrification of 

 air where the water was caught in a basin 

 about 90 cm. below the mouth of the 

 funnel). But when the funnel was slanted 

 so that the whole shower of drops from 

 the jet, or even a small part of it, struck 



* Keh-in, Maclean, Gait, ' On the Diselectrification 

 of Air.' Proc. Roy. Soo., >Iarch 14, 1895. 



