225 
Royal Irish Academy, 
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. 
The author then alluded to the received opinion, that the Aurora 
Borealis is an electric discharge of considerable intensity 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 phsenomenon) 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 Nov, 1838, 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 was but little above the mean electric intensity of that hour 
during the month ; from which the author inferred that this phse- 
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 experiments 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 
