AMERICAN 
JOURNAL OF SCIENCE AND ARTS, 
[THIRD SERIES] 
ART, XXVI.—Comparison of the mean daily range of the Mag- 
netic Declination and the number of Auroras observed each year, 
with the extent of the black spots on the surface of the Sun; by 
Exias Loomis, Professor of Natural Philosophy in Yale 
College. 
In a former number of this Journal (Sept., 1870), I instituted 
* Comparison between the mean daily range of the magnetic 
declination, and the number of auroras observed each year, an 
also with the extent of the black spots on the surface of the 
‘un. ‘That comparison appeared to me to establish a connec- 
tion between these three classes of phenomena, and indica 
at auroral displays at least in the middle latitudes of Europe 
and America are subject to the law of periodicity ; that their — 
grandest displays are repeated at intervals of about sixty years, 
and that there are also other fluctuations less distinctly marked 
Which succeed each other at an average interval of about ten 
4uroras by Prof. Joseph Lovering. This catalogue is contained 
im the Memoirs of the American Academy, vol. x. 
AM. Jour. So1.—Turrp Series, Vou. V, No. 28,—APRIL, 1873. 
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