100 COSMOS. 



recognized by Parry during his third voyage, and also, con 

 jointly with him, by Lieutenant Foster (1825) at Port 

 Bowen. The increase of intensity from morning till evening 

 in the mean latitudes has been made an object of the most 

 careful investigation by Christie, 17 Arago, Hansteen, Gauss, 

 and Kupffer. As horizontal oscillations, notwithstanding 

 the great improvements which have been made in the present 

 day in the dipping-needle, are preferable to oscillations of the 

 latter kind, it is not possible to ascertain the horary varia- 

 tion of the total intensity without a very accurate knowledge 

 of the horary variation of the dip. The establishment of 

 magnetic stations, in the northern and the southern hemi- 

 sphere, has afforded the great advantage of yielding the 

 most abundant, and, incomparatively, the most accurate 

 results. It will be sufficient here to instance two points of 

 the earth's surface, which are both situated without the 

 tropics, and almost in equal latitudes on either side of the 

 equator namely, Toronto, in Canada, 43 39' N. lat., and 

 Hobarton, in Van Diemen's Land, in 42 53' S. lat., with a 

 difference of longitude of about 15 hours. The simultaneous 

 horary magnetic observations belong at the one station to 

 the winter months, while at the other they fall within the 

 period of the summer months. While measurements are 

 made at the one place during the day, they are being simul- 

 taneously carried on at the other station for the most part 

 during the night. The variation at Toronto is 1 33' West ; 

 at Hobarton it is 9 57' East ; the inclination and the inten- 

 sity are similar to one another ; the former is, at Toronto, 

 about 75 15' to the north, and at Hobarton about 70 34' to 

 the south, whilst the total intensity is 13'90 in the absolute 

 scale at Toronto, and 13 '5 6 at Hobarton. It would appear 

 from Sabine's investigation, that these well-chosen stations 

 exhibit 19 four turning points for the intensity in Canada, and 

 only two such points for Van Diemen's Land. At Toronto, 

 the variation in intensity reaches its principal maximum 

 at 6 P.M., and its principal minimum at 2 A.M. ; a weaker 

 r; Christie, in the Phil Transact, for 1825, p. 49. 



18 Sabine, On Periodical Laws of the Larger Magnetic Disturbances, 

 in the Phil. Transact, for 1851, pt. i, p. 126, and on the Annnal Varia- 

 tion of the Magn. Declin. in the PhU. Transact, for 1851. pt. ii, p. 636. 



19 Observ. made at the Magn. and Meteorol. Observatory at Toronto, 

 vol. i (1840- 1842), p. Ixii 



