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 electricity, 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 of leaf 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 



