MAGNETIC INCLINATION. 107 



flipping needles, as well as the variation in the intensity of 

 the total force, consequently present principal and secondary 

 maxima or minima, and generally some of either type, which 

 therefore constitutes a double progression with four turning 

 hours (the, ordinary case), and a simple progression with two 

 turning hours, that is to say, with a single maximum and a 

 single minimum. Thus, for instance, in Van Diemen's Land, 

 the intensity or total force exhibits a simple progression, com- 

 bined with a double progression of .the inclination, while at 

 one part of the northern hemisphere, which corresponds ex- 

 actly with the position of Hobarton, namely, Toronto, in 

 Canada, both the elements of intensity and inclination ex- 

 hibit a double progression.* At the Cape of Good Hope 

 there is only one maximum and one minimum of inclination. 

 The horary periodical variations of the magnetic dip are a* 

 follows : 



I. Northern Hemisphere. 



Greenwich : Maxim. 9 A.M. ; minim. 3 P.M. (Airy, 01- 

 serv. in 1845, p. 21; in 1846, p. 113; in 1847, p. 247). 

 Inclin. in the last-named year, about 9 A.M., on an average 

 G8 59' 3"-, but at 3 P.M. it was 68 58 / G x/ . In the 

 monthly variation the maximum falls between April and 

 June, and the minimum between October and December. 



Paris: Maxim. 9 A.M.; minim. 6 P.M. This simple 

 progression from Paris and Greenwich is repeated at the 

 Cape of Good Hope. 



St. Petersburg : Maxim. 8 A.M. ; minim. 10 P.M. Va- 

 riation of the inclination the same as at Paris, Green wicli, 

 and Pekin ; less in the cold months, and the maxima more 

 closely dependent on time than the minima. 



Toronto: Principal maxim. 10 A.M.; principal minim. 

 4 P.M. ; secondary maxim. 10 P.M. ; secondary minim. 6 

 A.M. (Sabine, Tor., 1840-1842, vol. i., p. Ixi.) 



II. Southern Hemisphere. 



Hobarton, Van Diemen's Land : Principal minim. G A.M. ; 

 principal maxim. 11*30 A.M. ; secondary minim. 5 P.M.; 

 secondary maxim. 10 P.M. (Sabine, Hob., vol. i., p. Ixvii.). 

 The inclination is greater in the summer, when the sun is in 

 the southern zodiacal signs, 70 36 / -74 ; it is smaller in win- 

 ter, when the sun is in the northern signs, 70 34''66. The 

 annual mean taken from the observations of six years gives 

 * Sabine, Holarton, vol. i., p. Ixvii., Ixix. 



