112 Major-General Sabine on the Cosmical Features 



of the four quarters of the globe, in the tropics as well as in the 

 middle latitudes, and in both hemispheres ; and it will be seen 

 that the divergence of either the unbroken or the broken curve 

 at any particular hour is substantially the same in all the figures. 

 There is another kind of semiannual inequality, also therefore 

 attributable to solar influence, which I am unwilling to pass 

 without notice even in this brief review, as it has been satis- 

 factorily traced, admits of simple representation, and is perhaps 

 particularly likely to be suggestive to some among my hearers. 

 In this case I have to speak of the two other magnetic elements, 

 the intensity of the magnetic force, and the dip (or inclination 

 below the horizontal line) of the magnetic needle when free to 

 move in the vertical plane ; and I am not here concerned either 

 with their variations in the diurnal period, or with the transitory 

 disturbances which may affect them. Both the dip of the needle 

 and the intensity of the force acting upon it can be determined 

 with much precision when proper instruments are employed, and 

 the observers are well trained. Such determinations, made on 

 stated days in each month, have been continued for several years 

 at some stations, without any change either of instruments or of 

 observers; and it has been found that in the high or middle 

 latitudes of both hemispheres there occurs a small increase 

 both in the dip and in the force in the months when the sun is 

 nearest to the earth as compared with the months when his 

 distance from our planet is greatest, i. e. that both the dip and 

 the total force are greater in both hemispheres in December 

 than they are in June. This effect cannot, of course, be ascribed 

 to any influence of the seasons of summer and winter affecting 

 either the earth or the needle by their different temperatures ; 

 for the magnetic difference is the same in both hemispheres, 

 while the seasons are opposite, the higher force and dip of De- 

 cember being associated with winter in our hemisphere and 

 with summer in the southern hemisphere. The amount of the 

 difference, though small in itself, is large when tested by the 

 amount of probable error. It was first shown by the concurrent 

 testimony of several years of observation at Toronto in Canada, 

 and Hobarton in Tasmania. The observations of the five years 

 since the Kew Observatory has been in action have furnished 

 for the northern hemisphere a full corroboration of the inference 

 from the results at Toronto. It would be very desirable to have 

 a similar corroboration of the results at Hobarton, by equally 

 careful observations continued for a few years at some other 

 station in a similar latitude in the southern hemisphere. 



III. When a mean of the undisturbed observations at each 

 hour is taken for the entire year, the semiannual inequality of 



