May i6, 1895] 



NA TURE 



69 



Invariably the elect r<jn«;ler showed very high positive in fine 

 weather, before and during east wind. It generally rose very 

 much shortly before a slight puff of wind from that quarter, and 

 continued high till the breeze would begin to abate. I never 

 once observeil the electrometer going up unusually high during 

 fair weather without east wind follt^wing immediately. One 

 evening in August I did not perceive the east wind at all, when 

 warned by the electrometer to expect it ; but I took the j^re- 

 caution of bringing my boat up to a safe part of the beach, and 

 immediately found liy waves coming in that the wind must be 

 blowing a short distance out at sea, although it did not get so far 

 I as the shore. . . . On two different mornings the ratio of the 

 I house to a station about sixty yards distant on the road beside 

 I the sea was '97 and '96 respectively. On the afternoon of the 

 Ilth instant, during a fresh temporary breeze of east wind, 

 blowing up a little s[iray as far as the road station, most of 

 which would fall short of the house, the ratio was I 'oS in favour 

 of the house electrometer — both standing at the time very high — 

 the house about 350'. I have little doubt but that this was owing 

 to the negative electricity carried by the spray from the sea, which 

 would diminish relatively the indications of the road electro- 

 meter." 



§ 10. The negative electricity spoken of in this last sentence, 

 "as carried by the spray from the sea," was certainly due to the 

 inductive effect of the ordinary electrostatic force in the air close 

 above the water, by which every drop or splash breaking away 

 from the surface must become negatively electrified ; but this 

 only partially exjilains the difference which I observed between 

 the road station and the house station. We now- know, by the 

 second of l.enard's twti discoveries, to which I have alluded, 

 that every drop of the salt water spray, falling on the ground or 

 rocks wetted by it, must have given positive electricity to the 

 adjoining air. The air, thus positively electrified, was carried 

 towards and over the house by the on-shore east wind which 

 was blowing. Thus, while the road electrometer under the 

 spray showed less electrostatic force than would have been found 

 in the air over it and above the spray, the house electrometer 

 showed greater electrostatic force because of the positively elec- 

 trified air blown over the house from the wet ground struck by the 

 spray. 



§ II. The strong positive electricity, which, as described in 

 my letter to Joule, I always found in Arran with east wind, 

 seemed at first to be an attribute of wind from that (juarter. 

 But I soon found that in other localities east wind did not give 

 any very iiotalJe augmentation, nor perhaps any augmentation 

 at all, of the ordinary fair weather positive electric force, and 

 for a long time I have had the impression that what I observed 

 in this resjject, on the sea-beach of Brodick Bay in .\rran, was 

 really due to the twelve nautical miles of sea between it and the 

 Ayrshire coast east-north-east of it ; and now it seems to me 

 more ])robabIe than ever that this is the explanation when we 

 know from Lenard that the ctnmtlcss breaking waves, such as 

 even a gentle east wind produces over the sea between Ardrossan 

 and Brodick, must every one of them give some positive elec- 

 tricity to the air wherever a spherule of spray falls upon unbroken 

 water. It becomes now a more and more interesting subject for 

 observation (which I hope may be taken up by naturalists having 

 the opportunity) to find whether or not the ordinary fine weather 

 positive electric fi)rce at the sea coast in various localities is in- 

 creased by gentle or by strong winds from the sea, whether 

 north, south, east or west of the land. 



§ 12. From Lenard's investigation we now know that every 

 drop of rain falling on the ground or on the sea,* and every 

 drop of fresh water spray of a breaking wave, falling on a fresh 

 water lake, sends negative electricity from the water surface t() 

 the air ; and we know that every drop of salt water, falling on 

 the sea from breaking waves, sen<ls positive electricity into the 

 air from the water surface. Lenard remarks that more than 

 two-thirds of the earth's surface is sea, and suggests that break- 

 ing sea-waves may give contributions of positive electricity to the 

 air which may possibly preponderate over the negative electricity 

 given to it from other sources, and may thus be the determining 

 cause of (he normal fair weather positive of natural atmospheric 

 electricity. It seems to me highly probable that this pre]-)onderance 

 is real for atmospheric electricity at sea. In average weather, 

 all the year rt)und, sailors in very small vessels are more wet by 

 sea-spray than tiy rain, and I think it is almost certain that more 

 IWsitive electricity is given to the air by breaking waves than 



" " Uclicr die Electricilftt dcr W.-isserfalle." AnnaUti tier Physik unit 

 Cktinie, 1892, vol. xlvi. p. 631. | 



NO. I 



J>JO> 



VOL. 



5-^] 



negative electricity by rain. It seems also probable that the 

 ix),sitive electricity 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 quickly 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 

 normal fair weather positive, after the smaller positive or the 

 negative atmospheric electricity of broken weather, which was first 

 found by Beccaria in Italy I20years ago, and which has been amply 

 verified in Scotland and England,* could not be accounted for by 

 ]xisitively electrified air coming from the sea. Even at Beccaria's 

 (Jbservatory, at Garzegna di .Mcjndovi in Piedmont, or at Kew, 

 or Greenwich, or (Glasgow, we should often have to wait a very 

 long time for reinstatement of the normal positive after broken 

 weather, if it could only come in virtue of ])ositively electrified 

 air blowing over the place from the sea ; and several days, at 

 least, would have to pass before this result could possibly be 

 obtained 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 w eather ]wsitive. 

 Kain or snow, condensing out of the air high-up in the clouds, 

 must itself, 1 believe, become negatively electrified as it grows, 

 and must leave positive electricity 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 electri- 

 fied : 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 before it 

 lost water from its composition. Several times within the la.st 

 thirty years I have made imperfect and unsuccessful attempts to 

 verify this hypothesis by laboratorj- experiments, and it still 

 remains unproved. But I am much interested just now to find 

 some degree of observational confirmation of it in Elster and 

 Oitel's large and careful investigation of the electricity produced 

 in an insulated basin by rain or snow falling into it, which they 

 described in a communication published in the Silzungsbcrichte 

 of the \'ienna Academy of Sciences, of .May 1890. They 

 find generally a large electrical 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 the whole, a 

 preponderance of negative electrification. 



§ 14. But my subject this evening is not merely natural 

 atmospheric electricity, although this is certainly by far the most 

 interesting to mankind of all hitherto known effects of the 

 electrification of air. I shall conclude by telling you very 

 briefly, and without detail, somvlhing of new experimental results 

 regarding electrification and diselectrification of air, found 

 within the last few months in our laboratory here by Mr. 

 Maclean, Mr. Gait, and myself. We hope before the end of the 

 ]iresent session of the Royal .Society to be able to communicate 

 a sufficiently full account of our work. 



§ 15. :\\r blown from an uninsulated tube, so as to rise 

 in bubbles through pure water in an uninsulated vessel, and 

 carried through an insulated pipe to the electric receiving 

 filter, of which I have already told you, gives negative electricity 

 to the filter. With a small quantity of salt dissolved in the water, 

 or sea water substituted for fresh water, it gives positive electricity 

 to the air. There can be no iloubt but these results are due to 

 the same physical cause as Lenard's negative and positive 

 electrification of air by the impact of drops of fresh water or of 

 salt water on a surface of water or wel solid.. 



§ 16. A small quantity of fresh water or salt water shaken 

 up vehemently with air in a corked bottle electrifies the air, fresh 

 water negatively, salt water positively. A "Winchester quart" 

 bottle (of which the cubic contents is about two litres and a 

 half), with one-fourth of a litre of fresh or salt water poured into 

 it, and closeil by an india-rubber cork, serves verj- well for the 

 experiment. .After shaking it vehemently till the whole water is 

 filled with fine bubbles of air, we leave it till all the bubbles 

 have risen and the liijuiil is at rest, then take out the cork, put 

 in a metal or india-rubber pipe, and by double-acting bellows, 

 draw off the air and send it through the electric filter. We find 

 the electric effect, negative or positive according as the water is 

 fresh or salt, shown very decidedly by the quadrant electrometer : 

 and this, even if we have kept the bottle corked for two or three 

 minutes after the liquid has come to rest before we take ouf the 

 cork and draw oft' the air. 



§ 17. .-\n insulated spirit lamp or hydrogen lamp being con- 

 " " Electrostatics and Magnetism," xvi. § 287. 



