Methods for Observing Atmospheric Electricity. 275 



a degree of insulation in all weathers, by which there need not be more 

 than five per cent, jier hour lost by it from the atmospheric apparatus at 

 any time. A little attention to keep the outer part of the conductor 

 clear of spider lines is necessary. The apparatus I employed at 

 Invercloy 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 

 two feet and a-half from the wall, and nearly on a level with the window- 

 sill. The divided ring electrometer 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 13;j° to 14° of torsion required to bring the index 

 to zero, when urged aside by the electro-motive force of ten zinc-copper 

 water cells. The Leyden phial held so well that the sensibility of the 

 electrometer, measured in that way, did not fall more than 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 elec- 

 tro-motive force per foot of air, measured horizontally 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 

 fresh temporary breeze from the east. What I had previously ob- 

 served 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 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 electro- 

 meter 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 wind must be 

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

 the shore. 



The electrometers referred to in tlie preceding statement were on 

 two different plans. The first, or" divided ring electrometer," consists 

 of — (1,) A ring of metal divided into sectors, of which some — one or 

 more — are insulated and connected with the conductor to be electri- 

 cally tented, and the remainder connected with the earth. (2.) An 



