JI.VY 31, 1895.] 



SCIENCE. 



593 



comparatively small amount when there 

 was no obstruction to the shower between 

 the mouth of the funnel and the catching 

 basin 90 cm. below it. We intend to con- 

 tinue the investigation, with the shower 

 falling freely far enough down from the 

 mouth of the funnel to make quite sure 

 that the air which we draw off fi-om any 

 part of the funnel is not sensiblj' affected 

 by impact of the drops on anything be- 

 low. 



§ 9. The other discovery * of Lenard, of 

 which I told you, is that the negative elec- 

 trification of air, in his experiments with 

 pure water, is diminished greatly by very 

 small quantities of common salt dissolved 

 in it, that is brought to nothing bj- .011 per 

 cent.; that positive electrification is produced 

 In the air when there is more than .011 per 

 cent, of salt in the water, reaching a maxi- 

 mum with about 5 per cent, of salt, when 

 the positive electrical effect is about equal 

 to the negative efl"ect observed with pure 

 water, and falling to 14 per cent, of this 

 amount when there is 25 per cent, of salt 

 in the solution. Hence sea-water, contain- 

 ing as it does, about 3 per cent, of common 

 salt, may be expected to give almost as 

 strong positive electrification to air as pure 

 water would give of negative in similar cir- 

 cumstances as to commotion. Lenard in- 

 fers that breaking waves of the sea must 

 give positive electricity to the air over 

 them; he finds, in fact, a recorded observa- 

 tion by Exner, on the coast of Ceylon, 

 showing the normal positive electric poten- 

 tial of the air to be notably increased bj' a 

 storm at sea. I believe Lenard's discovery 

 fullj- explains also some very interesting 

 observations of atmospheric electricitj' of 

 mj' own, which I described in a letter 

 to Dr. Joule, which he published in tlie 

 Proceedings of the Literary and Philo- 



* ' Ueber die Electricitiit der Wasserfiille.' Table 

 xvii. p. S^H. Aiindhn der Phj/sik und Chemie, 189-2, 

 vol. xlvi. 



.sophical Society of Manchester for Octo- 

 ber 18, 18.59.* "The atmospheric effect 

 ranged from 30° to about 420° [of a heteros- 

 tatic toi'sion electrometer of ' the divided- 

 ring ' species] during the four days which I 

 had to test it ; that is to say, the electro- 

 metric force per foot of air, measured hori- 

 zontally from the side of the house, was 

 from 9 to above 126 zinc-copper water cells. 

 The weather was almost perfectly settled, 

 either calm, or with slight east wind, and 

 in general an easterly haze in the air. 

 The electrometer twice within half an hour 

 went above 420°, there being at the time a 

 fi-esh temporary breeze ft-om the east. 

 What I had previou.sly observed regarding 

 the effect of east wind was amply confirmed. 

 Invariably the electrometer showed very 

 high positive in fine weather, before and 

 during east wind. It generallj- 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 observed the electrometer going up 

 unusuallj- high during fair weather without 

 east wind following 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 

 precaution of bringing mj^ boat up to a safe 

 part of the beach, and immediatelj- found 

 l)j' waves coming in that the wind must be 

 blowing a short distance out at sea, al- 

 though it did not get so far as the shore 

 .... On two different mornings the ratio 

 of the house to a station about sixty yards 

 distant on the road beside the sea was .97 

 and '96 respectivelj'. On the afternoon of 

 the 11th inst, during a fresh temporary 

 breeze of east wind, blowing up a little 

 spraj' as far as the road station, most of 

 which would fall short of the house, the 

 ratio was 1 .08 in favour of the house electro- 

 meter — ^both standing at the time very 



* Republished in 'Electrostatics and Magnetism.' 

 ' Atmospheric Electricity, ' xvi. J 202. 



