ON THE PERIODICITY OF THE AURORA BOREALIS. 



221 



The days signalized by the frequency of these phenomena are November 12 and 13, 

 August 10, April 9 and 10, December 13, November 27, 28, and 29, January 1 and 2 

 (all of which days according to Quetelet are distinguished by extraordinary numbers 

 of shooting stars), and especially July 17. Baumhauer takes advantage of the fact that 

 fire-balls, &c. are often surrounded, when they first appear, with a cloudy envelope. As 

 nickel and magnetic iron enter largely into the composition of meteoric stones, he 

 concludes that these substances are also one principal ingredient in the lighter matter 

 which remains suspended in the air without falling to the earth. Hence he conjectures 

 that this floating matter will be magnetized by the earth, arrange itself everywhere 

 parallel to the resultant of the terrestrial magnetic forces at each place, and manifest 

 itself, when from any cause rendered luminous, as the Aurora Borealis or Australia 

 Baumhauer thinks it desirable that the ground in high latitudes should be searched for 

 nickel, since it is distributed so sparingly over the earth's surface that its presence at 

 any place might be taken as a safe indication of meteoric materials. He adds that this 

 hypothesis as to the origin of northern lights is sustained by the observations of Colla, 

 Wartmann and Quetelet, who have pointed out the fact (?) that the times when the 

 northern lights are most abundant coincide with the periods of greatest meteoric dis- 

 plays. Baumhauer modestly allows that his speculation in regard to the mutual 

 dependence of various classes of phenomena in the Sun's system, viz., shooting stars, 

 the fall of meteoric stones, and the northern lights, is only an attempt to introduce 

 some order into what has been hitherto an immense chaos of facts. 



Wolf has supplemented from his own learning the catalogue of meteorites and fire- 

 balls, made by Kamtz and Biot. 1 He assigns to each clay its proper number and pub- 

 lishes the following monthly means : 



Wolf selects the following days as conspicuously marked by the frequency of these 

 occurrences : January 2 and 10; February 4, 6, and 18; March 1 and 31; April 9, 10, 

 and 19 ; June 7 ; July 17 and 29; August 3, 5, 7, 8, 10 and 11; September 1 and 13 ; 

 October 1 and 3 ; November 9, 11, 12, 13, 16, 19 and 29; December 2, S, 11, 13, and 

 30 ; " also namentlich auch die Tage, welche sich constant oder wenigstens in einer grb's- 



1 Vierteljahrssclirift der Naturforsch. Gesellschaft in Zurich. Jakrgang I. 322-32. 



