OF THE AURORA BOREALIS ON THE MAGNETIC NEEDLE. 
105 
A proper value will now be put on the results obtained by Captain Franklin 
and Lieutenant Hood, chiefly at Fort Enterprise. They observed a remark- 
able disturbance of the needle when the Aurora passed the zenith ; that is, 
when the fringes came into the plane of the dip, which is there 86° 59'. But 
the full admission of this fact does not invalidate the results of an apparently 
opposite nature obtained by others, or their importance. The observations I 
made on the 21st, 22nd, and 26th of September, 1st, 3rd, 11th, and 25th of 
October, and the 17th, 18th, and 19th of November last, and now of the 20th 
December, show, that with very brilliant Aurora, there is no disturbance of the 
needle, if the fringes do not come into the plane of the dip. 
It is evident that as the needle is affected in those places only where the 
fringes are in that plane, observers in different latitudes may obtain very dis- 
cordant results on the same evening. The numerous observations collected by 
Mr. Dalton, of the appearances of Aurora on the 29th March, 1826, (Phil. 
Trans. 1828,) prove that many fringes of streamers may be parallel to each 
other at remote distances ; and the observation, by the President of the Royal 
Society, of a luminous arch in Cornwall, 29th September, 1828, simultaneously 
with a remarkable Aurora of many arches over the whole of Aberdeenshire, 
proves that the meteor is sometimes active over a space nearly coincident with 
the extent of this kingdom ; and we have no reason to suppose it may not ex- 
tend often much further. There might therefore be an extensive succession of 
observations of disturbance and non-disturbance of the needle, at the same 
instant, from N. to S., over many degrees of latitude. Next to the discovery 
of the truth, it will give me the highest satisfaction if the Royal Society shall 
be of opinion, that the result of the observations they have enabled me to make, 
is to reconcile the conflicting statements made regarding this matter, leaving 
unimpeached the accuracy of all the observers. 
The observations of the intensity, on the 19th December, lead now more 
plainly to the inference, that it is decreased under the influence of an arch of 
Aurora in the plane of the dip ; but the indications of decrease are too small to 
be fully confided in, until after a long series of similar results. 
I consider Mr. Paull’s observation on the evening of the 20th December, 
viewed in conjunction with mine, of great importance in various respects. The 
same Aurora that I saw here under an angle not exceeding 20° high, he saw at 
MDCCCXXX. 
P 
