222 ON THE PERIODICITY OF THE AURORA BOREALIS. 



sern Anzahl von Jahren besonders reich an Sternschnuppen zeigten." Neither the 

 days nor the months which are stamped with a deficiency or a superabundance of auroras 

 reappear in these new phenomena as equally memorable. 



Wolf 1 has arranged a collection of 5764 auroras, according to the days and months of 

 the year. He has then constructed three curves : 1, the first according to the twelve 

 monthly means ; 2, the second according to the daily numbers ; 3, the third according 

 to means of each five successive days, giving six ordinates for every month. His max- 

 ima derived from the latter curve are near March 20 and October 15, and the minima 

 near June 22 and December 25. The jaggedness of the second curve he attributes 

 mainly to accidents of observation, remarking, however, that January 3 and 6, February 

 11 and 22, March 26 and 29, May 1, September 24, November 2, and December 20, are 

 rich compared with the curve of monthly means; while February 14 and 21, March 31, 

 October 28, and November 5 and 28 are comparatively lean. Moreover the third curve 

 mounts unusually high during the first week of January and of July, that i*, shortly 

 after the periods of minima, and exhibits unusual depressions near the end of April and 

 November. But these subordinate waves, which ride the back of the great yearly swell 

 as a deferent, do not seem to me to point with any certain aim to the times for shoot- 

 ing stars and, through them, to the ring of meteors and the zodiacal lights. "Wolf 

 compares his Northern Light curve with the yearly changes of Magnetic Inclination as 

 found by Hansteen, of magnetic storms as studied by Sabine, and of Solar Spot' fre- 

 quency 2 and Magnetic Declination as developed by his own researches, and he 

 declares in favor of a prevailing agreement between them as exact as can be expected 

 from the nature of the observations. 



" Diese Ver<deichung zeigt, dass im Allgemeinen wirklich eine so grosse Uebereinstimmung zwischen den verschie- 

 denen Curven herrscht, als nur inimer bei der Natur der zu Grunde gelegten Beobachtungsreihen erwartet wcrden 

 kann, und wenn das erste Maximum der Nordlichtcurve vergleiekungsweise etwas friihe, das zweite etwas spat einzu- 

 treten scheint, so ergibt sich hiefur eine einfache Erklariing aus dem Zunehmen der Tageslange im Friihjahr und dem 

 Abnelimen der Tagesliinge im Herbst, — ebenso fur das relative Yerfriihen der beiden Minima's aus der durckscknitt- 

 lieh ungiinstigeren Witterung urn die Zeit der Solstitien. Auch die grosse Differenz zwischen den beiden Minima's der 

 Nordlichtcurve wird offenbar dureh die Verkaltnisse der Tageslange ungemein begiinstigt." 



A. de la Rive argues in favor of some association between appearances of the aurora 

 and lunar halos, rain, snow, &c. 



" Revenant b. la coexistence des particules glace'es dans l'air avee les aurores, nous en trouvons une preuve frappante 

 dans les observations faites au Canada et aux Etats-Unis. Des registres d'observations mete'orologiques, tenus avec beau- 



1 Vierteljahrsschrift der Naturforsch. Gesellschaft in Zurich. Jahrgang II. 372, 3. 



2 Vierteljahrsschrift der Naturforsch. Gesellschaft in Zurich. Jahrgang I. 161, 263, and 269. 



