402 Results of Makeestoun Observations, 1844. 



of magnetic disturbances ; the latter have their greatest value near the equinoxes, and their least value near 

 the solstices. 



When the numliers for 1844 are comhined with reference to the moon's age into four quarters, two of 

 which have the epochs of new and full moon in the middle, we obtain the average for each day of the moon's 

 age as follows : — 



27''- 3<i New Moon,... 0-40. 4*- 11*.. . 0-75. 12^-18'' Full Moon,... 0-86. 19'»-26'>... 1-38. 



The same law of variation is obtained from the 91 aurora; seen between January 1843 and June 1848; 

 these give the following mean nmubers : — 



27'>-3'' New Moon,... 1-90. 4'i-ll*...2-62. 12*-18'i Full Moon,... 3'43. 19d_26'i... 400. 



If we suppose that the number of aurorje should be the same at all ages of the moon, then we would 

 expect, that on account of the great number of famt auroras rendered invisible by the moonlight, the greatest 

 nmnber would be seen about new moon. This is not the case ; the greatest number has been seen in the quarter 

 intenne<liate between full moon and new moon ; and this conclusion, it is believed, will be obtained Irom 

 larger series of observations. Since, then, the greatest number of am-ora; are seen between full and new moon, 

 it is certain that the gi-eatest number occur nearer full moon than the epoch of visible maximum ; and it is pro- 

 bable tliat the greatest number actually occurs at full moon, though the moonlight will always render a direct 

 determination of the fact impossible.* It appears also from Table LXI., that the greatest numbers of aurora; 

 occur before midnight. As actual measures of the intensity cannot be easily taken, it can only be stated as a gene- 

 rally observed fact, that the maximum brilliancy of aurora; occurs between 8^ and 11'' p.m. Both the probable re- 

 sult for the moon's age and the other result for the diurnal law, agree with the laws deduced for the magnetic 

 disturbance in the preceding pages ; the magnetic disturbance is a maximum at full moon, and the (hsturbance 

 of the direction of the magnetic force is a maximum about 9'' 10™ p.m., the time of maximum frequency and 

 intensity of the aurora ; there can be little hesitation, therefore, in saying, that the laws of the aurora borealis 

 may be concluded fi-om those for the magnetic disturbance, and vice versa. In every case of observed dis- 

 turbance, including disturbances of the most minute character, in the year 1844, when the sky was sufficiently 

 free from clouds and moonlight, and twilight absent, the aurora was seen ; this remark, I believe, will apply 

 to the observations in other years . It is difficult, indeed, to understand the cause of the doubt which remained 

 so long with respect to the fact of this simultaneity ; some farther evidences of its generality may be noticed at 

 another time. 



* It is worth referring to the past year, as giving an illustration of the law of aurora and disturbance, as related to the moon's 

 age. The following is a list of all the aurorse seen at Malserstoun, in the year between the solstices of 1847 and 1848 : — 



1847. Aug. 22. Faint Aurora, 3 days before Full Moon. 



Sept. 27. Brilliant Aurora, 3 ... after 



... 29. Idem. 5 ... after 



Oct. 24. Idem. 1 ... after 



Nov. 19. Idem. 3 ... before 



Dec. 20. Idem. 1 ... before 



1848. Feb. 20. Idem. 1 ... after 



... 21. Idem. 2 ... after 



... 22. Idem. 3 ... after 



Mar. 17. Faint Aurora, 2 ... before 



19. Brilliant Aurora 



... 21. Idem. 2 ... after 



... 24. Faint Aurora, 5 ... after 



Apr. 17. Brilliant Aurora, 1 ... before 



29. Rather Faint Aurora, 11 ... after 



May 10. Faint Aurora, 8 ... before 



18. Brilliant Aurora 



The aurorae marked brilliant were the most beautiful and vivid, despite the moonlight, ever observed at Makerstoun, and they 

 were accompanied by magnetic disturbances of the same character, — the largest, it is believed, ever observed. 



Neglecting the faint aurora?, it wiU be seen that in 8 lunations brilliant aurora? were observed within three days of full moon, 

 only one brilliant aurora having been seen at Makerstoun farther from full moon, — namely, that of September 29. It is conceived 

 that these observations of themselves give a graa-t probabilit}/ to the conclusion, that the maximum for the aurora and magnetic dis- 

 turbance is at full moon. It is not, of course, supposed that brilliant auroras occur only near full moon, but that they occur more 

 frequently at that than at any other epoch : it should be remembered that what may be considered a vivid aurora in the absence 

 of moonlight, would become faint in its presence, and vice vena. 



