Iniellic/ence and Miscellaneous Articles. 543 



away with in my apparatus at the rate of five per cent, per half 

 second, or even faster. Hence a very moderate degree of insulation 

 is sensibly as good as perfect, so far as observing the atmospheric 

 eiFect is concerned. It is easy, by my plan of drying the atmosphere 

 round the insulating stems by means of pumice-stone moistened 

 with sulphuric acid, to ensure a degree of insulation in all weathers, 

 by which not more than five per cent, per minute will be lost by it 

 from the atmospheric apparatus at auy time*. A little attention, to 

 keej) the outer part of the conductor clear of spider lines, is necessary. 

 The apparatus I employed at luvercloy stood on a table beside a 

 window on the second floor, which was kept open about an inch to 

 let the discharging tube project out without coming in contact with 

 the frame. The nozzle was only about 2| feet from the wall, and 

 nearly on a level with the window-sill. The divided ring electro- 

 meter stood on the table beside it, and acted in a very satisfactory 

 way (as I had supplied it with a Leyden phial consisting of a 

 common thin white glass shade, which insulated remarkably well, 

 instead of the German glass jar — the second of the kind which I had 

 tried, and which would not hold its charge for half a day). 



I found from 13i-° to 14° of torsion required to bring the index 

 to zero when urged aside by the electromotive force of ten zinc- 

 copper water-cells. The Leyden phial held so well, that the sensi- 

 bility of the electrometer measured in that way did not fall more 

 than from 13|° to 13|° in three days. 



The atmospheric effect ranged from 30° to above 420° during 

 the four days which I had to test it ; that is to say, the electromotive 

 force per foot of air, measured horizontally from the side of the house, 

 was from 9 to 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 freah temporary 

 breeze from the east. What I had previously observed regarding 

 the effect of east wind was amply confirmed. Invariably the electro- 

 meter 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 observed the electi'ometer going up 

 unusually 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 my boat up to a safe part of the 

 beach, and immediately found, by waves coming in, that the east 

 wind must be blowing a short distance out at sea, although it did 

 not get so far as the shore. 



I made a slight commencement of the electro-cjeodesy which I 

 pointed out as desirable at the British Association, and in the course 

 of two days, namely, October 10th and 11th, got some very decided 



* In reality, when good glass stems are used, there need not be more 

 than 5 per cent, per hour of loss by imperfect insulutiou. 



