186 Mr. P. E. Chase on the Influence of 



its orbit, the diurnal variation being subject to an inequality 

 depending on the sun's declination. The diurnal range is 

 greater when the sun has north declination, and smaller when 

 south declination, the phenomenon passing from one state to 

 the other about the time of the equinoxes." (Part 2. p. 10. See 

 also Toronto Observations, 2. xvii. ; St. Helena Obs. 2. cxviii.) 



II. "At the hour of 6 or 7 in the morning the annual varia- 

 tion is a maximum, disappearing at a quarter before 10 a.m., 

 and reaching a second (secondary) maximum value at 1 p.m. 

 It almost disappears soon after 5 p.m., and a third still smaller 

 maximum is reached after 9 p.m. Half an hour before mid- 

 night, the. annual variation again disappears. At (and before 

 and after) the principal maximum between 6 and 7 in the morn- 

 ing, the annual variation causes the north end of the magnet to 

 be deflected to the east in summer and to the west in winter; at 

 1 p.m. the deflections are to the west in summer and to the east 

 in winter. The range of the diurnal motion is thus increased in 

 summer and diminished in winter — the magnet being deflected 

 in summer more to the east in the morning hours, and more to 

 the west in the afternoon hours, or having greater elongations 

 than it would have if the sun moved in the equator. In winter 

 the converse is the case." (Ibid. p. 12. Compare St. Helena 

 Obs. 2. cxviii.; Toronto Obs. 1. xiv. and 2. xvi.) 



III. "According to the same authority [General Sabine], the 

 annual variation is the same in both hemispheres, the north end 

 of the magnet being deflected to the east in the forenoon, the 

 sun having north declination ; while in the diurnal variation the 

 north end of the magnet at that time of the day is deflected to 

 the east in the northern hemisphere, and to the west in the 

 southern hemisphere ; in other words, in regard to the direction 

 the law of the annual variation is the same, and- that of the 

 diurnal variation the opposite in passing from the northern to 

 the southern magnetic hemisphere." (Ibid. p. 13. Compare 

 St. Helena Obs. 2. lxxx. cxviii.) 



IV. " The regular progression of the monthly values is a feature 

 of the annual variation deserving particular notice. There is no 

 sudden transition from the positive to the negative side, or vice 

 versa 1 , at or near the time of the equinoxes (certainly not at the 

 vernal equinox) ; on the contrary, the annual variation seems to 

 be regular in its progressive changes. The method here pursued 

 is entirely different from that employed by General Sabine for 

 the same end, but the results are, nevertheless, in close accord- 

 ance." It has been found that, the transition takes place " ten 

 days after either equinox, and also that the turning-points occur 

 ten days after the solstices." (Ibid. p. 14. Compare St. Helena 

 Obs. 2. cxx.) 



