MAGNETIC DECLINATION NEAE THE MAGNETIC EQUATOR. 673 



2d, The principal maximum occurs in the six months of April to September 

 at about 7 a.m., and the principal minimum occurs about twenty minutes past 

 noon in the same months. 



3d, Nearly the inverse of this happens in the four months of November to 

 February, inasmuch as the principal minimum occurs between 7 h 10 m and 7 h 20 m 

 a.m., and the principal maximum occurs betwixt l h 45 m and 3 h p.m. 



4th, When we examine the mode in which this inversal takes place in the 

 mean curves, it appears to happen in two ways: — 1st, In a direct transition 

 during the month of March from a minimum to a maximum at 7 a.m. ; and 

 during the month of October from a maximum to a minimum at the same hour ; 

 in which transitions the mean movement must necessarily at one time become 

 zero about the critical hour. 2d, In an apparent shift of the time of the afternoon 

 maximum. 



5th, The principal minimum, it has been noticed (2d), occurs in the months of 

 April to September within a few minutes of twenty minutes past true noon ; 

 this minimum never wholly disappears in the mean curves at Trevandrum. 

 Owing to the change going on in the law of variation in the months of March 

 and October, it happens about 30 m before noon in the latter month, when it is still 

 the principal minimum, and about one hour after noon in the former, when it is 

 a secondary minimum; it appears as a slight minimum, or as inflexion only 

 in the curves, for the four months of November to February. This conservation 

 of the noon minimum would seem to prove that there is no real inversion at this 

 hour, and that the minimum near noon and the maximum after noon are two dis- 

 tinct and independent phenomena, the former becoming more and more marked 

 from January to July. 



6th, The conservation of a minimum near noon in the six months of October to 

 March, has, as a consequence, the appearance of a secondary maximum, or an 

 inflexion of this character betwixt 7 a.m. and noon — generally near 10 a.m. 



7th, The principal maximum occurs betwixt l h 45 m and 3 h p.m. in the four 

 months November to February ; in March and October it happens near 3 h 30 m p.m.; 

 and in the remaining six months of April to September, from 4 h 20 m to 5 h 30 m p.m. 



8th, A quite secondary minimum occurs near 6 p.m. (or almost exactly at sun- 

 set) in the six months of October to March ; and a more marked minimum ap- 

 pears in the curves for the six months from April to September between 8 h and 

 9 h 30 m p.m. A faint minimum can be traced in the curves for the remaining six 

 months, October to March, at nearly the same hour ; so that the minimum at sun- 

 set is a phenomenon independent of that near 9 p.m. 



9th, The north end of the needle moves between 8 p.m. and 7 a.m. towards the 

 east in the five months May to September ; it moves towards the west between 

 the same hours in the four months November to February; whereas in the 

 months of March, April, and October, the change from one direction to another 



VOL. XXIV. PART III. 8 U 



