234 



ON THE PERIODICITY OF THE AURORA BOREALIS. 



E x = 1732.823 + x. 11.119 + 1.621 sin. (146° +x -tt-)+ 1-405 sin. [230° + a; — - ]. 



10 



This was afterwards changed to the following : — 



360 360° 



E x = 1799.455 + x. 11.153+ 1.621 sin. [290° + x — ] + 1.405 sin. [302° + * — -]. 



10 •-> 



Wolf makes the uncertainty in a single epoch by the usual formula, « = y — — -, 



equal to 1.575 years for the periods of minima, and 1.870 years for the periods of 

 maxima. The uncertainty in the value of the mean period is by the maxima alone 

 equal to .418 of a year, and by the minima alone equal to .336 of a year, according to 



the usual formula, r= \/~^~' 



TABLE LIV. 



Wolf says of his last formula : — 



" Iinrnerhin gebe ich sie nur als einen ersten Versueh, und behalte mir vor, in der Folgezeit, sei es ihre Constanten 

 nock etwas abzuandern, sei es dureh Zufugen weiterer Glieder ein nock besseres Anschmiegen zu erzielen." 



What gave extraordinary interest to these two apparently insulated discoveries, the 

 first in the Physics of the Globe and the second in Astronomy, was the additional one 

 that they were intimately associated with each other, the maximum of magnetic dis- 

 turbance occurring simultaneously with the maximum frequency in the solar spots. 

 This latter discovery was made almost at the same time by Sabine, Wolf, Secchi, 2 and 

 Gautier, 3 though Gautier admits that Sabine had the priority in time. With Sabine, 



i Predicted. 2 Arago, Astronomie, II. 180. Pogg. Ann. der Physik und Chemie, CXVII. 503. 



8 Biblioth. Univ. Archiv. de Nat. et Phys. Sei. XX. 189, XXXVI. 185. Also, Bib. Univ., Nouvelle Period II. 365, and V. 296. 



