Peoceedings of tee PoLYTECir\'ic Association. 931 



I Electric Storms. 



Aurora lorealis lias so generally been accompanied and preceded 

 bj great disturbances of the magnetic needle, that it has been called 

 a magnetic phenomenon ; and the general operation which causes such 

 disturbance, as well as the remarkable effects upon the telegraph 

 wires, in sometimes neutralizing, and at others greatly augmenting 

 the force of the battery current, has been called a magnetic storm. 



I prefer to call it an electric storm, for it is no inore nor less than 

 an operation of atmospheric electricity, moving in alternate aiid 

 varying directions. 



Electricity passing a magnetized needle, in any direction except 

 in a line directly transverse to the magnetic meridian, always causes 

 it to div^erge more or less, as when a current passes through a galvano-' 

 meter coil ; it is, therefore, as much an electric phenomenon as the 

 deviation of the galvanometer, or as the battery current itself. We 

 might as well call a common thunder storm magnetic, for it produces 

 eifects in all respects similar, but still more energetic and rapid. 



Coincidence with Spots on the Sun. 



A peculiar and interesting circumstance appertaining to aurora, 

 is, their periodic coincidence with the appearance of spots on the sun. 



The records go to show that the two phenomena have their 

 maxima and minima nearly simultaneously. 



Commencing with the year 1763, the maxima of spots and of the 

 aurora appear in the following order : 



Maxima. 



17()3 to 1709 r, vears. 



1703 to 1779 10 " " 



1763 to 178S 9 " 



1763 to 1804 16 " 



1763 to 1816 12 " 



1763 to 1830 U " 



1763 to 1837 7 " 



1763 to 1848 11 " 



1763 to 1860 12 " 



The length of the periods varies from six to sixteen years. 



The sun evidently possesses powerful electro-dynamic properties, 

 as well as magnetic polarity. 



Although the forces which act upon the magnetic needle emanate 

 directly from the earth, and are probably induced, in part at least. 



