MAGNETIC OBSERVATIONS. 99 



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

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

 variation of the total intensity without a very accurate knowl- 

 edge of the horary variation of the dip. The establishment 

 of magnetic stations in the northern and the southern hemis- 

 phere has afforded the great advantage of yielding the most 

 abundant, and comparatively 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 al- 

 most in equal latitudes on either side of the equator — name- 

 ly, Toronto, in Canada, 43° 39 / N. lat., and Hobarton, in 

 Van Diemen's Land, in 42° 53 7 S. lat., with a difference of 

 longitude of about 15 hours. The simultaneous horary mag- 

 netic 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 simultaneously 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 intensity are similar to 

 one another; the former is, at Toronto, about 75° lo' to 

 the north, and at Hobarton about 70° 34 y to the south, 

 while the total intensity is 13-90 in the absolute scale at 

 Toronto, and 13*5G at Hobarton.* It would appear, from 

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

 hibit! 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 

 secondary maximum at 8 A.M., and a weaker secondary 

 minimum at 10 A.M. The intensity at Hobarton, on the 

 contrary, exhibits a simple progression from a maximum be- 

 tween 5 and 6 P.M. to a minimum between 8 and 9 A.M. ; 

 although the inclination there, no less than at Toronto, ex- 

 hibits four turning-points.J By a comparison of the varia- 



* Sabine, On Periodical Laivs of the larger Magnetic Disturbances, 

 in the Phil. Transact, for 1851, pt. i., p. 126; and on the Annual Va- 

 riation of the Magn. Declih., in the Phil. Transact, for 1851, pt. ii., p. 

 636. 



t Observations made at the Magn. and Metcorol. Observatory at To- 

 ronto, vol. i. (1840-1812), p. Ixii. 



% Sabine, in Magn. and Meteor. Observations at Hobarton, vol. i., p. 

 lxviii. "There is also a correspondence in the range and turning 

 hours of the diurnal variation of the total force at Hobarton and at 

 Toronto, although the progression is a double one at Toronto and a 



