594 



SCIENCE. 



[N. S. Vol. I. No. 22. 



high — the house about 350°. I have little 

 doubt but that this was owing to the nega- 

 tive electricity carried by the spray from 

 the sea, which would diminish relatively 

 the indications of the road electrometer." 



§ 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 electro- 

 static force in the air close above the water, 

 by which every drop or splash breaking 

 away from the surface must become nega- 

 tively electrified ; but this only partially 

 explains the difference which I observed 

 between the road station and the house 

 station. We now know, by the second of 

 Lenard's two 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 to- 

 wards 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 electrified air blowing over the 

 house fi-om the wet ground struck by the 

 spray. 



§ 11. 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 quarter. But I soon found that 

 in other localities east wind did not give 

 any very notable augmentation, nor per- 

 haps any augmentation at all, of the ordi- 

 nary fair weather positive electric force, and 

 for a long time I have had the impression 

 that what I observed in this respect, on the 

 sea-beach of Brodick Bay in Arran, 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 probable than ever that this is the ex- 

 planation when we know from Lenard that 

 the countless breaking waves, such as even 

 a gentle east wind produces over the sea 

 between Ardrossan and Brodick, must ev- 

 ery one of them give some positive elec- 

 tricity to the air wherever a spherule of 

 spray falls upon unbroken water. It be- 

 comes now a more and more interesting 

 subject for observation (which I hope may 

 be taken up by naturalists having the op- 

 poi'tunitjr) to find whether or not the ordi- 

 nary fine weather positive electric force 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 everj' drop 

 of fi'esh water spray of a breaking wave, 

 falling on a fresh water lake, sends negative 

 electricity from the water surface to the air ; 

 and we know that every drop of salt water, 

 falling on the sea from breaking waves, 

 sends 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 breaking 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 the nor- 

 mal fair weather positive of natural atmos- 

 pheric electricity. It seems to me highly 

 probable that this preponderance is real for 

 atmospheric electricity at sea. In average 

 weather, all the year round, sailors in very 

 small vessels are more wet by sea-spray 

 than bj' rain, and I think it almost certain 

 that more positive electricity is given to the 

 air by breaking waves than negative elec- 



* ' Ueber die Electricitat der Wasserfiille. ' Annal- • 

 en derPhysik %md Chemie, 1892, vol. xlvi., p. 631. 



