Atmospheric Origin of the Aurora, §c. 159 
ced before them all; and find, in the relative temperatvres re- 
quired for them, a rogpoboration of the conclusion. drawn from 
the time of the mancooding storm in relation to their — 
heights in the air. 
The absolute temperature is, for the seasons of their occur- 
rence, low for all, and of itself affords evidence of the existence 
of crystals. Frota semi-monthly observations for five years, on 
two springs at Schenectady, I have inferred, that the mean tem- 
perature of the earth there is 48.8°; and this accords nearly with 
the mean temperature of the air in’ that vicinity for the last ten 
years. Should we make allowance for the daily mean, and for 
the mean seasons of the year in which the aurora occurs, we 
should have a still more just and striking view of the cold usu- 
ally required for its production. The barometer rises and. the. 
thermometer falls before an aurora, and the mean length of time 
is about two days; and consequently these changes commence 
about four days before the storm, or about. three and a baal days 
when there are not two auroras in succession. : 
-'This affords one of. the earliest and surest’ prognostics of the 
storm, and is-more to be relied on than even the subsequent de- 
pression of the barometer, which, in modern times at least, seems 
solely to have attracted attention. It would be curious, (though 
it is perhaps improbable, and I have not seen the original,) if this 
early ascent of the barometer were that alluded to in the long 
since banished rule of Pascal. Though this patriarch of, this 
branch of science may, as is alledged, have fallen into a grave 
error in regard to this, yet there will be revived a certain modifi- 
cation of his rule, that the batomefer rises" before a storm; and 
perhaps he may be aig zesceghe? the citron and aise nt be the ori 
ginal discoverer 
That the changés of pressure and temperature ‘Giiaiinee he 
fore the’aurora, accords with the above theory. They are to be’ 
regarded as among the causes rather than the effects of the au- 
rora, Yet that they continue a little beyond the time of it, I 
have long since observed, and expressed it by the rule, that the | 
barometer is usually es ‘and the nacemoncgg! falling, on the 
evening of ai aurora. - 
Within a few years, an interesting Retnsas of the above 
theory; so far, at least, as to the fact of a connexion between at- 
mospheric arial and magnetism, has been presented in many in- a 
