> | a 
Aimospheric Origin“of the Aurora, §c. 151 
spread more rapidly than a small one, advancing like a wave, 
overtaking and absorbing those waves which had begun to spread. 
from a@ smaller nucleus. This induction, or the influence of a 
crystalline mass, in disposing particles and small crystals which 
are in its vicinity, but at'some visible distance from it, to unite 
with each other, was still more evident from observing on the 
screen the existence and motions of scattered clusters composing 
a. darkly dotted border or penumbra, skirting the darker image of 
the general crystalline mass already formed, and regularly advan- 
cing before it across the screen. Perhaps we should hardly be 
justified in calling such phenomena magnetic; yet it would be 
easy to show that these and manyother phenomena exhibited by 
microscopic crystals, are regulated by laws strikingly anelogous 
to those of magnetic induction.’ 
The above phenomena may be shown with great distinetnbas 
in tincture of camphor, sufficiently diluted to make the process 
slow. 
If the electricity of. scant water is ever sietieniail with 
magnetism, it must be during the perfect crystallization in 
elevated regions of auroral action, where the circumstances are 
favorable to the perfection both of the process and the products. 
The rarity of the vapor there is favorable to a regular aggregation 
of the molecules, and the cold is intense. During crystallization, 
the temperature of the crystal might rise to 32°, by the evolution 
of latent heat, and soon afterwards sinking perhaps 100°, to the 
“ original temperature of the vapor. For such immense and instan= 
taneous changes, a less elevation in the air is requisite in the 
higher latitudes ; and there, it appears from observation, that the 
aurora iapifiie teas elevated. It is unnecessary to cite the numer-— 
ous authorities which exist, to prove the occasional lowness of the 
aurora in high latitudes. Mr. Trevelyan observed, that in Faroe 
and the Shetland islands, it was often seen not more than forty 
or fifty feet above the sea, and learned, that in both countries it 
is frequently heard. One person had perceived in it, when red, 
an electrical smell.* 
In our latitude, the aurora is seician at great heights. On this 
subject the anthor’s views seem to have been misapprehended. 
Some of the intimate connections which he has proved to exist, 
* Edinb. Philos. Jour. vii, 182. 
