1832] WRITINGS OF JOSEPH HENRY. 59 



magnetic influence of the aurora; and in the scientific ex- 

 peditions under Capt. Parry to the north, in the peculiar 

 regions, as it would appear, of this meteor, no unusual dis- 

 turbance of the needle was observed to accompany the au- 

 rora, although the apparatus was visited every hour in the 

 day, and sometimes oftener, when any thing rendered it 

 desirable. Indeed, so far from producing a disturbing effect, 

 Dr. Brewster concludes, from a comparison of the observa- 

 tions, that the aurora, in the arctic regions, seems rather to 

 exercise a sedative influence.* 



On the other hand. Dr. Richardson states, from his own ob- 

 servations, made at Bear Lake, during six successive months 

 of the years 1825-6, and again in 1826-7, that the aurora 

 does influence the magnetic needle. "A careful review of 

 the daily register," says he, " has led me to form the follow- 

 ing conclusion : That brilliant and active coruscations cause 

 a deflection of the needle almost invariably, if they appear 

 through a foggy atmosphere, and if prismatic colors are ex- 

 hibited ; on the contrary, when the atmosphere is clear, and 

 the aurora presents a dense steady light of a yellow color, 

 and without motion, the needle is often unafiected."t 



In this state of knowledge, every additional fact becomes 

 of some importance. The following communication, it is 

 therefore hoped, may be useful, either in directing the atten- 

 tion of observers in this country to the subject, or in corrob- 

 orating similar observations made in other quarters of the 

 globe. 



In September, 1830, 1 commenced a series of observations, 

 for Professor Renwick, of Columbia College, to determine the 

 magnetic intensity at Albany. In the course of these, I un- 

 expectedly witnessed a disturbance of the magnetism of the 

 earth, in connection with an appearance of an aurora, which 

 on some accounts appears interesting. 



The needles used in these observations were those men- 

 tioned in Capt. Sabine's letter to Prof. Renwick, published 



* Edinburgh Philosophical Journal of Science, vol. 8. 

 f Edinburgh New Philosophical Journal, vol. 5. 



