OF THE AURORA BOREALIS ON THE MAGNETIC NEEDLE. 
103 
now detailed, afford a proof, — a negative one indeed, and therefore imperfect, 
bnt now very extensive, — that the needle is not affected by the Aurora, till it 
comes into the plane of the dip : and we have thus, I trust, an explanation of 
the discordant results obtained and announced regarding this matter by diffe- 
rent former observers. When the disturbance has been observed, there have 
been no doubt zones of Aurora in the plane of the dip, though perhaps obscure 
and liable to be overlooked. Most of those I observed in that position on the 
14th were so faint, that I might not have noticed some of them, had I not traced 
their progress southward from stations where they were much more brilliant. 
It would be as yet premature to infer any connection between the easting 
and westing of the declination, and the vividness of the fringes in their eastern 
or western ends. What occurred at 8 p. m. and \ past 10 p. m. might lead 
us to suspect that the needle declines towards the most vivid end. 
In regard to the intensity, I cannot venture to say, that the slight decrease 
indicated at \ past 10 is not an error of observation ; being conscious that the 
limits of errors of this kind ought not to be taken at less than the change then 
noted. I could not take the intensity at f past 6, when the declination was 
greatest, from a desire to watch the extent of the change in declination pro- 
duced by the Aurora, of which I was for the first time fully assured. When I 
receive the separate apparatus for the intensity, with which I am to be favour- 
ed, I shall expect more certain results on that point. 
Alford , December '26th, 1829. — Since I addressed you on the 15th current, I 
have made some additional observations on the Aurora borealis, of which I 
proceed to put you in possession in continuation. 
From Journal of observations. 
Frost during the 16th, 17th, and 18th Dec. Therm, at night 19°. 
19th Dec. — 10 p. m. Bar. 29°.7- Therm. 30°. — At past 11 p. m. a 
heavy low fog cleared up, and exposed a very brilliant Aurora. An arch of very 
brilliant streamers about 25° high over dense clouds in the N. A broad lane 
of clear sky above these from W. to N. E. Over head many broken clouds 
giving partial views of a narrow arch of Aurora from E. to W. in the plane of 
the mag. dip, and many streamers approaching the zenith from N. To the S. 
