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like common air, excellent non-conductors,* and, mixing 
with the air of the room, give a preponderance of positive 
influence to the testing insulated flame (that is to say, 
render the air potential positive at the place occupied by this 
flame). 
Half an hour, or often much more, elapses after such 
an operation, before the natural negatively electrified air 
becomes again paramount in its influence on the testing 
flame. 
That either positive or negative electricity may be carried, 
even through narrow passages, by air, I have tested by 
turning an electric machine, with a spirit lamp on its prime 
conductor, for a short time in a room separated from the 
lecture room by an oblique passage about two yards long, 
and then stopping the machine and extinguishing the lamp, 
so as to send a limited quantity of positive electricity into 
the air of that room. When the lecture room window was 
kept open, and the door leading to the adjoining room shut, 
the testing spirit lamp shotved the natural negative. When 
the window was closed, and a small chink (an inch or less 
wide) opened of the door, the indication quickly became 
positive. If the door was then shut, and the window again 
opened, the natural effect was slowly recovered. A current 
of air, to feed the lecture room fire, was found entering by 
either door or window when the other was shut. This 
alternate positive and negative electric ventilation may be 
* I find that steam from a kettle boiling briskly on a common fira is an 
excellent insulator. I allow it to blow for a quarter of an hour or more 
against an insulated electrified conductor, without discovering that it has any 
effect on the retention of the charge. Tho electricity of the steam itself, in 
such circumstances, as is to be expected from Faraday’s investigation, is not 
considerable. Common air loses nearly all its resisting power at some tem- 
perature between that of boiling water and red hot iron, and conducts 
continuously (not, as I believe, is generally supposod to be tho case, by 
disruption) as glass does, at somo temperature below tho boiling point, with 
so great ease as to discharge any common insulated conductor almost com- 
pletely in a few seconds. 
