May 31, 1895.] 



SCIENCE. 



595 



tricity by raiu. It seems also probable that 

 the positive electricitj' from the waves is 

 much more carried up by strong winds to 

 considerable heights above the sea than 

 the negative electricity given to the air by 

 rain falling on the sea ; the greater part of 

 which may be quicklj' lost into the sea, and 

 but a small part carried up to great heights. 

 But it seems to me almost certain that 

 the exceedingly rapid recovery of the nor- 

 mal fair weather positive, after the smaller 

 positive or the negative atmospheric elec- 

 tricity of broken weather, which was first 

 found bj' Beccaria in Italy 120 years ago, 

 and which has been amply verified in Scot- 

 land and England, ^could not be accounted 

 for by positivelj- electrified air coming from 

 the sea. Even at Beccaria"s Observatory, at 

 GarzegTia di Mondovi in Piedmont, or at Kew 

 or Greenwich or Glasgow, we should often 

 have to wait a veiy long time for reinstate- 

 ment of the normal positive after broken 

 weather, if it could only come in virtue of 

 positively electrified air blowing over tlie 

 place from the sea; and several days, at 

 least, would have to pass before this result 

 could possibly be detained in the centre of 

 Europe . 



§ 13. It has indeed always seemed to me 

 probable that the rain itself is the real 

 restorer of the normal fair weather positive. 

 Raiu or snow, condensing out of the air 

 higli up in the clouds, must itself, I believe, 

 become positivelj' electrified as it grows, 

 and must leave jjositive electricitj' in the 

 air from which it falls. Thus rain falling 

 from negatively electrified air would leave it 

 less negatively electrified, or non-electrified 

 or positively electrified ; rain falling from 

 non-electrified air would leave it positively 

 electrified ; and rain falling from positively 

 electrified air would leave it with more of 

 positive electricity than it had befoi-e it 

 lost water from its composition. Several 

 times within the last thirty years I have 



*' Electrostatics and Maj;iieticism,' XVI., J S^"". 



made imperfect and unsuccessful attempts 

 to verify this hypothesis bj' laboratory ex- 

 periments, and it still remains unproved. 

 But I am much interested just now to find 

 some degree of observational confirmation 

 of it in Elster and Geitel's large and care- 

 ful investigation of the electricity produced 

 in an insulated basin by rain or snow fall- 

 ing into it, which they described in a com- 

 munication published in the Sitzungsberiehte 

 of the Vienna Academy of Sciences, of May, 

 1890. They find generally a large electri- 

 cal effect, whether positive or negative, by 

 rain or snow falling into the basin for even 

 so short a time as a quarter of a minute, 

 with however, on a whole, a preponderance 

 of negative electrification. 



§ 1-t. But my subject this evening is not 

 mereh- natural atmospheric electricity, al- 

 though this is certainly by far the most 

 interesting to mankind of all hitherto known, 

 effects of the electrification of air. I shall 

 conclude bj' telling you very briefly, and 

 without detail, something of new experi- 

 mental results regarding electrification and 

 diselectrification of air, found within the 

 last few months in our laboratorj- here by 

 Mr. Maclean, Mr. Gait and myself. "We 

 hope before the end of the present session 

 of the Royal Society to be able to communi- 

 cate a sufficiently full account of our work. 



§ 15. Air blowTi from an uninsulated 

 tube, so as to rise in bubbles tlirough 

 pure water in an uninsulated vessel, and 

 carried through an insulated pipe to the 

 electric receiving filter, of which I have al- 

 ready told you. gives negative electricity to 

 the filter. With a small quantity of salt 

 dissolved in the water, or sea water sub- 

 stituted for fresh water, it gives positive 

 electricity to the air. There can be no 

 dt)ubt but these results are due to the same 

 phj'sical cause as Lenard's neg-ative and 

 positive electrification of air by the impact 

 of di-ops of fresh water or of salt water on a 

 surface of water or wet solid. 



