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. 
