158 Atmospheric Origin of the Aurora, §c. 
was in a single instance, and that on the occasion of two con-_ 
secutive auroras, the latter tending to prolong and increase the 
clearness. This instance being omitted—as it should be—the 
decrements of clearness during the 24 hours succeeding the au- 
rora are to the increments, as 112 to 1, the increment having 
been in one instance one tenth; and the whole decrement in 
thirty instances, 112 tenths. On none of the eight instances in 
which there were auroras on two consecutive nights, had the 
cloudiness increased on the evening of the second, as compared 
with that of the first. The mean decrement of clearness for the 
remaining 24 instances, was .46. Hence, to give a popular state- 
ment, approximately true—the. evening of an aurora is, on an 
average, twice as Clear as the succeeding evening, unless another 
aurora occurs on the latter; in which case, the sky continues 
equally clear. As the forenoon succeeding an aurora is in.gene- 
ral unusually clear, this great decrement of clearness usually takes 
place‘in' a ad hours, whilst ths: increments had required. several 
YS... 
he following table,. (abotranted from those on which the nine 
propositions are Faia ,) shows the mean temperatures at 9 P. M. 
of the days of the different meteors, and on the evenings one and 
two days previous ; also the mean number of days previous, when 
———— - — oes en PRE commenced.* 
= aae ~~ ag ag] «es 
= eee 38 : a : oa 7 ~s Sy oea 
Names of as meteors 2a S ee ie # Ee 23 ges 
ae , cal ee oo FS ee ee Se° | 333 
Bes | &F eS e2° | 2e¢ | age 
Sil a E a” | gee Lee 
Aurora Boreaus, | 40 | 44.9° | 44.19 | 42.5° | 2.16 1.95 
Polarized clouds; 22° |°40.5° | 37.2° | 36.2° | 1.90 | 2.92, 
Halos 17 | 33.8° | 29.6° | 28.9° | 2.09 | 2.30 
Vertical beams, » 4°>' 235° | 16.72 14.59 3.00_ 1.87 
“The nasi of vertical beams is so small, as to forbid wont 
dence in mean results as to elapsed time. In the case of the 
other meteors, we see a pretty near correspondence as to the 
times when the eemnnrannic and barometric iets weet 
ert as which, Speke inadvertence of an ‘inne: had crept into 
