344 



Aurora Borealis. 



A table of 184 aurorae seen at Makerstoun in years 1843 to 

 1849 is given in pages Ixxv,— Ixxviii. of Vol. xix., Part 2 ; from this 

 table the following results have been obtained : — 



A very careful outlook for aurorse was kept throughout the whole 

 period, but especially during the first five years ; an outlook warned 

 by magnetic disturbance in circumstances unfavourable to the visi- 

 bility of the meteor, and assisted by a practical acquaintance with the 

 faintest auroral indications. In several cases, the auroral appear- 

 ances were very faint ; these are entered in the table as " Traces," 

 and, in othei's, there was doubt whether the appearance was truly 

 auroral ; these are indicated by " Trace 1 " It should be noted that, 

 with the exception of the years 1844 and 1845, aurorse were seldom 

 looked for after midnight. 



Diurnal variation of frequency of the Aurora Borealis. — The 

 following are the numbers of times which aurorse were seen, at each 

 hour, from 5^ p.m. till S** a.m., for the whole period — referring to 

 the printed tables for the numbers for each season. 



Hour, 5^ 6^ 7^ Sh 9^ 10^ iV 12i> IS^^ 14:^ 15^ IG'^ IV^ 



No., 5 19 45 57 91 75 50 37 27 15 11 3 2 



The greatest number of auroree were seen at 9^* p.m. ; this i-esult 

 is independent of the effect of twilight, since 9^ p.m. is also the 

 hour of maximum frequency for the winter months. This hour 

 is nearly the hour of maximum disturbance for the magnetic de- 

 clination and dip ; as, however, the maximum disturbance of the 

 total magnetic force and a maximum of the magnetic dip appear to 

 occur about 5^ p.m., this also may be an epoch of maximum fre- 

 quency or intensity, though this can only be determined in higher 

 latitudes. It should also be remarked, that, since the epoch of 

 maximum disturbance varies with season, so, thei'efore, it is probable 

 will that of frequency of the aurora ; some traces of this may be de- 

 duced from the previous table. In the winter quarter, November- 

 January, four-fifths of the times at which auroree were seen were for 

 the hours before lO'i p.m., whereas in the spring quarter there were 

 only three-fifths seen before 10'' p.m. 



Annual Variation of frequency of the Aurora Borealis. — The 

 first line following contains the numbers of aurorse observed in each 

 month during the six complete years 1843-8, and the second line 

 gives the numbers of hours at which the aurora? were seen. 



