50 RESULTS OF METEOROLOGICAL OBSERVATIONS. 



maximum frequency about the autumnal equinox has long been Known, the dis- 

 covery of one or two distinct periods in the secular change is of more recent date ; 

 the shorter of these periods is expressed in the above numbers.^ 



' After writing the above paper Dr. R. Wolf's " Mitheilungen uber die Sonnenflecken," No. XIX 

 was received ; according to the investigations of Herr Fritz and of Dr. Wolf the two periods of the' 

 aurora borealis, from observations in the middle latitudes, are 55.6 years for the great period, and 

 11.11 years for the subordinate cycle. For comparison with the results given in the text, the years 

 of auroral maxima and minima since 1788, according to Fritz and Wolf, are appended: — 



Maxima. Minima. 



1788 principal 



1796 

 1804 



1811 principal 

 1816 



1S2S 

 1830 



1834 

 1839 



1842 

 1848 principal 



1856 

 1859 



It will be observed that the years of maxima observed at Brunswick accord, as well as can be 

 expected from a single locality, with these general results. The reader is also referred to Prof. 

 Loomis' account of the aurora borealis in the annual report of the Smithsonian Institution for 1865, 

 p. 208, and especially to the table p. 228. 



