AURORA BOREALIS. 229 



observed at Toronto, distant from Greenwich more than 3,500 miles. The 

 disturbances at Toronto commenced at nearly the same absolute time as at 

 Greenwich, and they were generally simultaneous at both stations. The same 

 extraordinary disturbance was noticed at St. Helena, distant from London 4,800 

 miles, and from Toronto 6,000 miles. A .similar disturbance occurred at the 

 Cape of Good Hope, still more distant, and also at Trevandrum, in India, which 

 is almost diametrically opposite to Toronto. This phenomenon was noticed 

 simultaneously over an entire hemisphere, and, not improbably, was sensible at 

 every* point of the earth's surface. 



At the same time there occurred an auroi'al display of unusual extent. An 

 aurora was observed throughout Canada and the northern parts of the United 

 States,* as well as in England and Norway, and alsd in the southern hemi- 

 sphere, at Van Dieman's Island. 



During the great auroral display of September 2, 1S59, the tlisturbances of 

 the magnetic needle were still more remarkable throughout North America, 

 Europe, and northern Asia, as well as in New Holland. At Toronto the de- 

 clination of the needle changed 3° 45' in half an hour. The inclination was 

 observed to change 2^ 49' when the needle passed beyond the limits of the 

 scale, so that the entire range of the needle could not be determined. The 

 horizontal force was observed to change to the extent of one-ninth of its whole 

 value when the needle passed beyond the limits of the scale, so that its entire 

 range could not be determined. t 



At Rome, September 2, at 7^' 10'" a. m., the declinometer pointed 2° 50' to 

 the west of its ordinary position. After this the needle returned rapidly to the 

 east, and at 7^ 30'" pointed 1^ 23' east of its mean position, thus describing an 

 arc of 4° 13' in one-third of an hour. The bitilar indicated a diminution of the 

 horizontal component amounting to about one-eighth of its mean value | 



At Paris the magnetic instruments were very much distm-bed, and were car- 

 ried beyond the range of their scales, so that the extreme range could not be 

 determined. § 



At St. Petersburg the declination of the needle changed 4° 24' Avhen the 

 needle passed beyond the range of its scale, so that the entire range could not 

 be determined. For a similar reason the entire change of the horizontal inten- 

 sity could not be determined. || 



At Christiania the variation of the horizontal intensity amounted to nearly 

 one-thirteenth of its whole value.^ 



At Melbourne, Australia, at the same time the magnetic instruments were 

 very much disturbed, the range of the declination being 1° 9', and that of the 

 horizontal intensity one-thirtieth of its whole value.** 



In the volume of the Greenwich Magnetical and Meteorological Observations 

 for 1862, Professor Airy has given an abstract of the magnetic observations 

 from 1841 to 1857, made on days of great magnetic disturbance. 



The magnetic force of the earth is resolved into forces acting in the direction 

 of three rectangular axes ; two of which lie in a horizontal plane, one pointing 

 north and south, the other east and west, while the third axis has a vertical posi- 

 tion. From Professor Airy's abstract, it appears that out of 170 magnetic 

 storms observed at Greenwich in seventeen years, 63 per cent, of the whole 

 number began with westerly force + 5 ^"^^ 60 per cent, ended with westerly 

 force + . Of the whole uumUer, 66 per cent, began with northerly force — , 



* Hough's N. Y. Met., p. 480. 



t American Journal of Science, n. s., v. 28, p. 390. 

 X American Journal of Science, n. s., v. 29, p. 397. 

 § Americfin Joirrnal of Science, n. s., v. 29, p. 39]. 

 II American Journal ot Science, n. s., v. 30, p. 80. 

 il American Journal of Science, n. s., v. 29, p. 387. 

 ** American Journal of Science, n. s., v. 3"2, p. 8. 



