1894.] and Inclination as exhibited on the Magnetarium. 211 



direct comparison of the declination periods at London and at the 

 Cape of Good Hope than was set forth in my former paper ; and, 

 secondly, to show a further agreement between the indications of the 

 magnetarium and the results of recent observations of the dip and 

 declination at the Island of Ascension. 



The rate of backward rotation of the internal electro-dynamic sphere, 

 as I have said, is 22*5 minutes = 0*375 annually. Now, the period 

 of the westerly march of the declination needle at London from zero 

 in the year 1657 to its maximum of 24 30' in the year 1817 is 

 160 years ; therefore, 0'375 X 160 = 60 of differential rotation of 

 the internal sphere. Again, the westerly march of the needle at the 

 Cape of Good Hope from the year 1609 to its maximum of 30 in the 

 year 1881 is 272 years. Therefore, 0'375 x 272 = 102 of differential 

 rotation of the internal sphere. Hence, 60 : 160 years : : 102 : 272 

 years ; the outward westerly declination periods at London and the 

 Cape of Good Hope respectively, as shown by observation and on 

 the magnetarium. Subjoined are tables of the declination and in- 

 clination at London, the Cape of Good Hope, and on the magnetarium 

 for the same epochs. 



Table I. Secular Changes of the Declination and Inclination 

 at London. 



ERRATUM. 



Page 210, line 7 from bottom. 

 For 20 C 30' read 23 Btf, 



