207 



repeated many times without renewing the positive elec- 

 tricity of the adjoining room by turning the machine afresh. 



The out of doors air potential, as tested by a portable 

 electrometer in an open place, or even by a water dropping 

 nozle outside, two or three feet from the walls of the lecture 

 room, was generally on these occasions positive, and the 

 earth's surface itself, therefore, of course, negative; — the 

 common fair weather condition, which I am forced to con- 

 clude is due to a paramount influence of positive electricity 

 in higher regions of the air, notwithstanding the negative 

 electricity of the air in the lower stratum near the earth's 

 surface. 



On the two or three occasions when the in-door atmo- 

 spheric electricity was found positive, and, therefore, the 

 surface of the floor, walls, and ceiling negative, the potential 

 outside was certainly positive, and the earth's surface out of 

 doors negative, as usual in fair weather. 



