ON THE PERIODICITY OP THE AURORA BOREALIS. 



219 



Boue 1 has labored assiduously to establish a connection, such as is implied in a com- 

 mon origin, between different portions of the Physics of the Globe, and, possibly besides, 

 between shooting stars and the zodiacal light. He questions the periodicity of the latter, 

 and claims no correspondence in the periods of shooting stars and the aurora. But he 

 argues earnestly, though in my opinion not very conclusively, in favor of some affiliation 

 between auroras and earthquakes. He quotes largely from the voluminous catalogues 

 of earthquakes published by Perrey in the Memoires de L'Academie Imperiale de 

 Dijon and elsewhere. Perrey has arranged his data by months, years, and centuries, 

 and finds some evidence of a secular period as well as of a yearly one. He also points 

 out a coincidence between the periodicity of earthquakes and the monthly tides, 

 the maximum appearing at syzygies and the minimum at quadratures. They are also 

 more frequent when the moon is near the meridian than they are when the moon is 

 90° from the meridian. The monthly change he has developed by a periodical function 

 similar to that which I have employed upon the aurora. Of the earthquakes which oc- 

 curred in France, Belgium, and Holland, Perrey has made the following distribution 

 among the months. 2 The second line of the table refers to earthquakes observed in 

 the Antilles; 3 the third line to those observed in the Isle of Zante; 4 the fourth to those 

 observed in Europe and the adjacent parts of Asia and Africa ; the fifth to those observed 

 in the Avhole of the Northern Hemisphere, as compiled by Mallet. 5 



The frequency of earthquakes varies from month to month, but there is no resem- 

 blance between the law which governs this change and the yearly course of the aurora, 

 or between the two sets of maxima and minima. The nearest approach to such an 

 agreement is in the summer minimum. Boue attaches value to the fact that out of three 

 hundred and fifty-one auroras observed by Hansteen and Herrick between 1837 and 

 1847, and four hundred and fifty-seven earthquakes compiled by Perrey, forty-seven cor- 

 respond in the day and five in the hour of the occurrence, and fifty more coincide in time 

 within one or two days. When Boue compared the same earthquakes with his own cata- 

 logue of eight hundred and eighty-three auroras, he found half of them to correspond 

 within a day or two to some aurora, and from eight to ten within a single hour. 



1 Sitzungsberichte (ler Kaiserl. Akad. iler Wissensch. XII. 459, 60. 



2 Mem. Couronn. et des Savans Etrang de l'Aead. Brux. XVIII. 97. 8 Mem. de l'Acad. ImpeV. de Dijon, for 1845,6, p.' 385. 

 • Mem. de l'Acad. Impe'r. de Dijon. Deuxieme Serie, XI. 103. 6 Report of the British Assoc., XXVIII. Meeting, pp. 28 and 57. 



