eae oe 
140 4 Miscellaneous Intelligence. 
80, naacee. it is probable will that € the frequency of the aurora ; some 
traces of this may be deduced from the previous table. In the winter 
quarter, November—January, four-fifihs of the times at which aurore 
were seen were for the hours before 10h P. M., whereas in the spring 
quarter there were only three-fifths seen before 10h P. M. 
Annual Variation of frequency of the Aurora Borealis.—The first 
line following contains the numbers of aurore observed in each month 
during the six complete years 1843-8, and the second line gives the 
numbers of hours at which the aurore were seen. 
Jan. Feb. March. April. May. June. July. Aug. Sept. Oct. Nov. Dec. 
15 16 26 1436 Se: 0.27. 18 ee ee 
50 62 oo 3948 6a U 0. 10 $2 “44 58 4 
The greatest repos of aurorz were observed in March for the first 
six months, and in October for the last six months of the year; none 
were observed in lone and July. hen the six months of 1849 are 
included, the number for February is twenty, -six, and for March twenty- 
eight. The law of visible frequency of the aurore is the same as that 
“deduced already for magnetic disturbance ; namely, maxima near the 
equinoxes, and minima near the solstices, the minimum at the summer 
solstice being the principal. As, however, the shortness of night during 
the summer months must diminish the number of visible aurore, it is 
by no means Seitto from these numbers that a minimum occurs at the 
the same diurnal law of frequency at all seasons of the year, the exist- 
ence of the summer minimum could be satisfactorily determined, by 
oats, 10h Pp. m.-2h a. M., during which (even in the months of August 
and May) there is little twilight to extinguish aurore. The numbers 
are as follow, for these five hours in each month of the years 1843-8: 
Jan. Feb, March. April. May. June. July.: Ang. Sept. Oct. Nov. Dec. 
15 24 38 31-3 TF 0 O 2) 14-16 38 12 
autumn months, showing the later epoch of the maximum frequency in 
the former. An examination, however, of the table for the disturbance 
of the magnetic: declination (Table 18, vol. xix., part 2,) will show that, _ 
r 
on ubt ; ; 
ber for August than for September and October, if there should bea. 
doubt in the case of May compared with April. The difference, how- — 
ever, even in the latter case is too great to be explained by any slight 
_shift of the epoch of maximum frequency in the two mont 
the ae it appears certain that a minimum of actual as well as as of 
visible frequency occurs in summer; a result quite in acco with 
