68 WRITINGS OF JOSEPH HENRY. [1832 



and that it again decreased, and was less than usual the next 

 morning at 7h. 20m. 



By adding five hours to the time of the observations made 

 at Albany, we shall have nearly the corresponding time at 

 Mr. Christie's residence in Woolwich. These times being 

 6h. and lOh. p. m. will therefore correspond with llh. p. m. 

 and 3h. a. m. of time at Woolwich. From this it appears 

 that the observations at Albany were made at a period of 

 absolute time between the last observation of Mr. Christie 

 on the evening of the 19th, and the morning of the 20th. 

 The only interesting result however which apparently can 

 be drawn from a comparison of the observations, is that at 

 both places there was a disturbance of terrestrial intensity 

 at the same time; the intensity rising above and sinking 

 below its usual state at each, although these changes did not 

 occur in the same order at both places. 



I am not aware that a simultaneous disturbance of terres- 

 trial magnetism, in connexion with an aurora, has ever be- 

 fore been noted at two places so distant from each other. 

 Nor do I think the co-incidence in this case in the least de- 

 gree accidental. On the contrary, it appears to me highly 

 probable that the disturbing cause was not only common to 

 both places, but was also active at the same time in a great 

 portion of the northern part of the globe. A brilliant au- 

 rora is by no means a local phenomenon. That of the 28th 

 of August, 1827, was visible over nearly the whole of the 

 northern States, in Canada, and also from some part of the 

 Atlantic ocean. But what places the extensive and simul- 

 taneous appearance of the aurora in a more striking point 

 of view than any in which it perhaps was ever before ex- 

 hibited, is the comparison of the notices of the aurora given 

 under the monthly meteorological reports in the Annals of 

 Philosophy for 1830 and 1831, and the Reports of the Re- 

 gents of the University of the State of New York for the 

 same period. By inspecting these two publications, it will 

 be seen that from April 1830 to April 1831 inclusive, the 

 aurora borealis was remarkably frequent and brilliant, both 

 in Europe and in this country ; and that most of the auroras 



