68 WRITINGS OP JOSEPH HENRY. [1832 



ON A DISTURBANCE OF THE EARTH S MAGNETISM, IN CONNEC- 

 TION WITH THE APPEARANCE OF AN AURORA BOREALIS, 

 AS OBSERVED AT ALBANY, APRIL 19tH, 1831.* 



(Silliman's American Journal of Science, April, 1832; vol. xxii,pp. 143-155.) 



That the aurora has some connection with the magnetism 

 of the earth, was asserted as early as the middle of the last 

 century; and since that time many observations have been 

 recorded tending to confirm this position. 1. It has been 

 observed that when the aurora appears near the northern 

 horizon in the form of an arch the middle of this is not in 

 the direction of the true north, but in that of the magnetic 

 needle at the place of observation, and that when the arch 

 rises towards the zenith it constantly crosses the heavens at 

 right angles, not to the true, but to the magnetic meridian. 

 This fact is most obvious where the variation of the needle 

 is great. 2. When the beams of the aurora shoot up so as 

 to pass the zenith, which is sometimes the case, the point of 

 their convergence is in the direction of the prolongation of 

 the dipping needle at the place of observation. 3. It has 

 also been observed that during the appearance of an active 

 and brilliant aurora the magnetic needle often becomes rest- 

 less, varies sometimes several degrees, and does not resume 

 its former position until after several hours. 



From the above facts, it has been generally inferred that 

 the aurora is in some way connected with the magnetism of 

 the earth; and that the simultaneous appearance of the me- 

 teor, and the disturbance of the needle, are either related as 

 cause and effect, or as the common result of some more gen- 

 eral and unknown cause. 



The subject is however involved in much obscurity; and 

 there are some facts which tend to throw doubt on the con- 

 nection of the two phenomena. The accurate and valuable 

 observations of Col. Beaufoy in England, continued for sev- 

 eral years, add nothing towards establishing the fact of the 



* Communicated to the Albany Institute, January 26, 1832. 



