Royal Irish Academy. 225 



hitherto employed, and exhibited a highly insulated galvanometer, 

 containing about three thousand turns of very fine wire covered 

 with silk, varnished and baked, — which instrument, although ex- 

 quisitely sensitive to the feeblest voltaic electricity, was not at all 

 acted upon by atmospheric electricity of the low tension which ex- 

 ists 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 author- 

 ities in Europe, yet he had reason to think that it had never, in 

 any country, been deflected 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 indi- 

 cated 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 al- 

 ways, when electrified, be a tangent to the ball terminating the 

 graduated rod. 



Tlie author then alluded to the received opinion, that the Aurora 

 Borealis is an electric discharge of considerable intensity occurring 

 near the polar regions, at gi-eat heights in the atmosphere, where 

 the air is necessarily rare, and where, consequently, the electric 

 light (as shown in our artificial imitation of the phsenomenon) must 

 be very much diffused and ramified. Hoping to tln*ow light upon 

 this subject, he had made a series of observations on tlie electric 

 intensity of the twenty-four hours, commencing at mid-day on the 

 12th of Nov, 18-38, and continued at intervals of fifteen minutes, — 

 except during the appearance of the Aurora, when they were made 

 every five minutes, and even oftener. The results of these observa- 

 tions were laid down in a chart, which exhibited the intensity of the 

 electric fluid during these twenty-four hours, a period including that 

 of the magnificent crimson Aurora, which was observed on the night 

 of the 12th, and morning of the 13th of November, 1838, over every 

 portion of the globe. It appeared, by this chart, that th(? electric 

 intensity during the existence of this magnificent display of Auroral 

 light Vv'as but little above the mean electric intensity of that hour 

 during the month ; from which the author inferred that this phe- 

 nomenon, if at all electric, occurred at such a distance as to be un- 

 able to affect the apparatus. 



The author then proceeded to give an account of the extended 

 series of exiDeriments which he had undertaken at the recommenda- 

 tion of the Academy, and which he had continued during twelve 

 months, at intervals of fifteen minutes, during at least ten days, and 



Phil. Mag. S. 3 Vol. 16. No. 102. March 1840. Q 



