«J. A. Lefroy on the Aurora Borealis of 1850-1851. 159 
The stations of observation inthe first'and second groups are 
not ‘yet numerous enough to decide the question, whether the 
aurora ever appears in the exterior when it is absent in the inte- 
ror circles, but in forming an opinion on the number whieh ex- 
tend from the interior to the exterior of them, we must not forget 
that, notwithstanding, the large number of observers, both regu- 
ar and occasional, in the third group, and their wide distribution, 
a considerable proportion of the entries in Table III, rest at pres- 
ent upon an observation at only one station,* and unless particu- 
lars are given, which is unfortunately not always the case, may 
be reasonably regarded as doubtful. - Where particulars are given 
there can be, of course, no doubt. : 
The observations made under direction of the Smithsonian In- 
stitution begin to be general in March, 1849, and the stations are 
so numerous that we ought, perhaps, to consider observations to 
have been possible every night. ‘Table III, has been made as 
complete as possible, by including some observations kindly eom- 
municated by Mr. Ei. C. Herrick, together with any that were 
found in the Regent’s reports for 1848-1849 of which particulars 
Were given, or which occurred at more than one station on the 
ber to March inclusive, 1850-1; that aurora was seep before mid- 
night within the first circle on 88°5 per cent. of practicable nights, 
in the second circle on 80 per cent., and in the third on only ‘ 
Per cent., indicating a rapid falling off of the causes producing it 
at distances exceeding 1600 miles from the magnetic pole. 
It is scarcely necessary to say that these simple numerical com- 
parisons are but the first fruits of the observations; such as they 
are, however, they suggest to the mind a spectacle which if true 
in nature, must be of wonderful magnificence. The polar light 
kindling on each meridian, as that of day declines, sometimes 
With the splendor of prismatic coloring over half a hemisphere ; 
sométimes contracting its circles and paling its fires, for a peri 
of days or weeks; and sometimes spreading downwards over the 
vated as is usually supposed, about a third of its light must be 
absorbed by the atmosphere. ‘To pt es 
details would lead me much beyond the limits of such a com- 
co ee eae ce 
OF the total damm ations in 1850, 54 are at one station only; 
of the total tumber ce Fg epee at present at one station only—the ma- 
pay ¢ of these in i The proportion to which any doubt can attach is 
