3y ON THE RECENT SECULAR PERIOD 



Taking later dates, let us compare the grand aurora described in CamdcriPuis- 

 tory of the Reign of Queen Elizabeth, which occurred in November, 1574, with that 

 of November, 1835, which it greatly resembled. We find the interval to be 261 

 years, and 4 periods, of 05 years each, make 260 years. Finally, if we take 1837 

 as the middle of the late return, and subtract from it 65 years, we are carried back 

 to 1772, which is about the middle of the next preceding period, which lasted from 

 about 1760 1 to 1783. By a continual subtraction of 65 years backwards from 1837, 

 we fall successively on periods of which we have no records of auroras. As in. the 

 case of HalLy's comet, auroral returns might have occurred, but passed into obli- 

 vion for want f historians. Still, by this process, we fall in with many periods of 

 auroras which iid not fail to arrest the attention of contemporary writers; we 

 annex a few examples : — 



1837 — 65=1772, the middle of the last return before the present. 



1772-65 1707, one of the Reprises of Mairan. 



1707-2x65 = 1577, the middle of a great period. 2 



From the foregoing and many similar inductions, I think it may be inferred with 

 considerable probability, that the greatest secular periods of the aurora borealis 

 occur at intervals of about 65 years, reckoning from the middle of one period to 

 the middle of another, although returns of a less remarkable character are probably 

 interspersed among these. 



The duration of one of these great periods appears to be from 21 to 25 years. 

 That which we have just passed through, commenced in 1827 ; and if we consider 

 it as completed in 1848, when there was almost a cessation of the phenomenon in 

 its higher forms for two years, its duration was 21 years. The occurrence of three 

 exhibitions of the first class, in September, 1851, and of one in February, 1852, 3 

 throws some doubt on this point. Although the greatly diminished intensity since 

 1848, would incline me to consider the period as terminating then, yet these later 

 exhibitions indicate a duration of 25 years. If we examine into the duration of 



1 A very inconsiderable aurora, which appeared at Philadelphia in November, 1757, is described as 

 a remarkable and an unusual occurrence; which shows that there had been for some time a period of 

 intermission of the phenomenon. — Bartrani's Letter to Dr. Franklin, Phil. Trans., V, 474. 



3 Mairan, p. 184. 



3 No aurora of the higher classes has appeared at New Haven since that of February, 1852, to the 

 present time, December 21st, 1855. In the Regents'' Report, for 1854, only four are recorded, all of which, 

 with one exception, were of the humbler forms ; whereas, in 1840, near the middle of our secular period, 

 the same publication contained accounts of seventy-five auroras for that year. 



I have recently been favored, through the kindness of Mr. M. H. Boye, of Philadelphia, with manu- 

 script notes, made by himself, by Mr. Charles Bullock, and by Mr. Isaac Lea, containing, severally, 

 interesting accounts of auroras of the higher classes, observed by them at later dates than any of this 

 description observed by myself. 



On the 11th June, 1852, Mr. Lea, while on a voyage to England, off Newfoundland, saw an aurora 

 which possessed so many remarkable features as to rank it in the first class. What was quite singular, 

 the exhibition began on the south, and streamers ascended finally from the entire circumference of the 

 horizon. It was also remarkable that streamers shot up from beloiv the dark segment. As late, also, 

 as Sept. 2d, 1853, Mr. Boye saw, off Cape Race, a splendid auroral exhibition which covered almost 

 all parts of the sky. From the drawings which he has been so kind as to send me, I infer that this also 

 must have been one of the higher class of auroras. 



