On Some Observations of Atmospheric Electricity. 91 



tive to high positive generally occur ; and during continuous 

 rain strong negative tension is frequently present, which 

 gradually gives place to an increasing positive one some little 

 time before the rain ceases. In very heavy rains, however, 

 the air seems to be reduced to zero, or the same potential as 

 the earth's surface. 



It has also been noticed that, if after continuous rain it 

 clears up, the setting-in of rain again is usually preceded by 

 a gradually increasing negative tension. Fogs are always 

 accompanied by a high positive condition. 



In the course of some experiments on a very fine day, for 

 the purpose of ascertaining the best position for placing the 

 collector of our electrometer, the following notable results 

 .were obtained : — The electric condition of the air being 

 normal (positive potential), when an insulated conductor 

 connected with the electrometer was rapidly raised from 

 the surface of the ground to the height of about 20 feet, 

 a large and rapid increase of positive electricity was shown ; 

 and when the conductor was as rapidly lowered, a corre- 

 sponding diminution was observed. If the conductor was 

 moved rapidly from south to north, keeping it at as nearly 

 the same height from the ground as possible, a strong 

 positive indication was noted, while moving it from north to 

 south the reverse took place. Moving it from east to west 

 gave strong positive, while moving it from west to east gave 

 a strong negative indication. 



In repeating these experiments a few days ago in a hot 

 wind, when the air had a strong negative potential, the 

 following results were obtained: — . 



Raising the conductor gave a strong negative indication, 

 and lowering it a strong positive. 



Moving the conductor from south to north gave a strong 

 negative, and from north to south a strong positive indica- 

 tion. Moving the conductor from east to west gave also a 

 strong negative, while moving from west to east gave a 

 strong positive indication. 



These results are exactly opposite to those obtained in the 

 first experiments, and can no doubt be accounted for by the 

 negative potential of the air which prevailed at the time. 



It must be remarked that in these experiments the indica- 

 tions of the electrometer took place during the motion of 

 the conductor, and that immediately the conductor was at 

 rest in its new position the reading of the electrometer 

 became normal for the position the conductor was then in. 



