202 
MR. FOX ON THE VARIABLE INTENSITY 
sent up streams of red and white light which occasionally nearly reached the 
zenith. These were most striking early in the evening, and more especially 
about eleven, or a little later, when the coruscations were beautiful. At 7 p.m.* 
I found the needles at 0, but soon after their north ends moved towards the 
east, and at 8 to 8^ their easterly variation was 1 ° 15 '. They began to return 
westward at 8f, and soon after 10 p.m. were again stationary in the magnetic 
meridian. At 11 to 11^ p.m., 1 found their intensity had diminished. Many 
instances are given in the table of the appearance of the aurora in the horizon 
about the magnetic north, and extending more or less considerably on each 
side of it. It was generally of a pale white, and sometimes I could perceive 
faint streams shooting upwards from the horizon a very few degrees, but more 
often I could not. It will be seen that considerable variations of the needle 
usually occurred in the course of the same evenings ; and sometimes these 
variations took place on evenings when I did not remark any luminous 
appearance in the northern horizon. 
All the variations at night were towards the east-f, whether the aurora was 
actually visible or not ; and hence may we not conclude, taking it for granted 
that it is an electrical phenomenon, and that it usually moves from about the 
north towards the south, that it must be of the nature of positive electricity ? 
And, by a parity of reasoning, may we not assume the existence of an opposite 
state of electrical action by day, in order to account for the diurnal westerly 
variation, which is most considerable in the summer in these latitudes, when 
the aurora prevails about the south pole ? This idea seems to be strengthened 
by a fact I have noticed, that the magnetic intensity is usually less considerable 
in summer before the middle of the day than it is afterwards ; so that the 
minimum intensity commonly occurs some hours before the maximum tem- 
perature. 
It is evident that the elevation of the aurora must often be exceedingly great, 
probably much more than a thousand miles, as it seems to be generally seen from 
places very distant from each other at the same time, and in nearly the same 
* I did not observe the needles before 7 p.m. 
-j- I have since observed a slight westerly variation in the needle at night, but this seems to be of 
rare occurrence. 
