Coast Lines and Magnetic Declination. 181 



On the Influence of the Configuration and Direction 

 of Coast Lines upon the Rate and Range of the 

 Secular Magnetic Declination. By Henry Wilde, 

 F.R,S. 



{Received April jrd, iSpj..) 



In a paper which was read before the Royal Society in 

 June, 1890, I showed that the principal phenomena of 

 terrestrial magnetism and the secular changes in its 

 horizontal and vertical components could be explained on 

 the assumption of an electro-dynamic substance (presumably 

 liquid or gaseous) rotating within the crust of the earth in 

 the plane of the ecliptic, that was to say, at an angle of 

 23°'5, and a little slower than the diurnal rotation. By 

 means of some electro-mechanism, new to experimental 

 science, which I termed a Magnetarium, the period of 

 backward rotation of the electro-dynamic sphere required 

 for the secular variations of the magnetic elements on 

 different parts of the earth's surface was found to be 960 



o 



years, or 22*5 minutes = 0*375 annually. 



From the relations of a magnetic needle on the earth's 

 surface, and an electric current circulating round the 

 internal electro-dynamic sphere, it will be obvious that the 

 magnetism of such a system would be symmetrically 

 distributed, with similar lines of declination and inclination 

 on meridians and parallels 180 from each other. An 

 examination, however, of the lines of declination over the 

 terrestrial globe, as determined by careful and repeated 

 observations, exhibits wide divergencies from the sym- 

 metrical lines of declination obtained with the electro- 

 dynamic sphere alone. 



Thus, there are on the variation chart (Plate X.) four 



