1832] WRITINGS OF JOSEPH HENRY. 67 



beams of auroral matter, were shooting up from every part 

 of the surface of the State of New York. 



But the most interesting circumstance in reference to this 

 aurora, is that which I have learned from the December num- 

 ber of the Journal of the Royal Institution of Great Britain, 

 viz., the fact of a disturbance of terrestrial magnetism being 

 observed by Mr. Christie in England, on the same evening, 

 and at nearly the same time the disturbance was witnessed 

 in Albany, and that too in connection with the appearance 

 of an aurora. 



Mr. Christie had adjusted a magnetic needle for the ex- 

 press purpose of observing the effect when an aurora should 

 appear, but was not so fortunate as to be able to make any 

 observations with it until the evening of the 19th of April. 

 His apparatus consisted of a light needle six inches long, 

 suspended within a compass box by a fine brass wire -g^ of 

 an inch in diameter, and twenty-three inches long. The 

 needle was deflected from the magnetic meridian by the re- 

 pulsive action of two bar magnets placed on opposite sides 

 of it; so that instead of pointing to the magnetic north, it 

 settled iu the direction of N. 37° W. As the needle assumed 

 this position in consequence of the attractive force of the 

 earth, and the repulsive force of the magnets, a deviation 

 from the north towards the west would indicate a diminu- 

 tion of the terrestrial horizontal intensity, and a deviation 

 towards the north an increase in that intensity, the intensity 

 of the magnets remaining the same. At 10 o'clock p. m. 

 on the evening of the 19th, during the appearance of the 

 aurora, Mr. Christie found the needle vibrating between N. 

 43° 40' W. and N. 42° 40' W. At lOh. 15m. its direction 

 was N. 34° W. It continued to approach the north until 

 lOh. 37|m. when it pointed N. 33° 30' W. It again receded 

 from the pole, and at lOh. 40m. vibrated between N. 37° W. 

 and N. 36° W. The next morning at 7h. 20m. the needle 

 pointed N. 40° W. From this brief abstract of Mr. Christie's 

 observations, it will be seen that the horizontal intensity was 

 less than usual at 10 o'clock; that it increased until lOh. 

 37Jm. when it was greater than in its undisturbed state; 



