214 Mr. II. Wilde. Variation of Magnetic Declination [Mar. 1, 



Table IV. Secular Changes of the Declination and Inclination at 

 the Cape of Good Hope on the Magnetarium. 



The secular changes of the magnetic elements at St. Helena are 

 interesting from the fact that the declination period agrees well with 

 the geographical position of this island, which is west of the meridians 

 of London and the Cape of Good Hope. 



The epochs of the zeros of the declination at these places are in the 

 order of their longitudes respectively, 



Cape of Good Hope 

 London 



St. Helena . 



long. 18 28' E. 1609. 



,,00 1657. 



5 43' W. 1683. 



As St. Helena w south of the equator, the outward westerly march of 

 the declination needle has a long period which is not yet completed 

 (prop. V). The length of this period, as shown on the magnetarium, 

 is 256 years, and will arrive at its maximum in the year 1939. 



Further proofs of the truth of the theory that the secular changes 

 in the magnetic elements are caused by the rotation of an electro- 



