365 
highly insulated galvanometer, containing about three thou- 
sand turns of very fine wire covered with silk, varnished 
and baked,—which instrument, although exquisitely sen- 
sitive to the feeblest voltaic electrieity, was not at all acted 
upon by atmospheric electricity of the low tension which 
exists during serene weather in this country. Mr. Clarke 
added, that although the application of such an instrument 
would be a great desideratum in experiments on atmospheric 
electricity, and in this point of view had been recommended 
by the highest scientific authorities in Europe, yet he had 
reason to think that it had never, in any country, been de- 
flected by atmospheric electricity in serene weather. 
The author then exhibited the electrometer which he 
had devised for, and used in his experiments on this subject. 
It consisted of a bell of glass, seven inches in diameter, 
through the side of which passed a sliding graduated rod, 
furnished with a vernier, which indicated the distance, in 
hundredths of an inch, through which a single pendent slip 
of leaf gold was attracted towards the rod which was in 
connexion with the earth. The slip ofleaf gold was attached 
to a vertical and well insulated rod, which passed through a 
collar of leathers, and could therefore be raised or depressed, 
as required by the varying intensity, so that the lower end 
of the leaf should always, when electrified, be a tangent 
to the ball terminating the graduated rod. 
The author then alluded to the received opinion, that the 
Aurora Borealis is an electric discharge of considerable in- 
tensity occurring near the polar regions, at great heights in 
the atmosphere, where the air is necessarily rare, and where, 
consequently, the electric light (as shown in our artificial 
imitation of the phenomenon) must be very much diffused 
and ramified. Hoping to throw light upon this subject, 
he had made a series of observations on the electric intensity 
of the twenty-four hours, commencing at mid-day on the 12th 
of November, 1838, and continued at intervals of fifteen 
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