THE BEARINGS OF MAGNETIC OBSERVATIONS. 93 



magnetism, why it is subject to solar diurnal, lunar diurnal, 

 sidereal diurnal and the other variations and disturbances, 

 nor the cause of magnetic storms, although we can observe 

 connections between them, earth currents, and aurorae. 

 Whether the causes of all these exist below the surface 

 of, or are external to, the earth, or are a combination of 

 the two, has still to be learnt, and it seems hardly too much 

 to hope that the restless needle will sooner or later be the 

 means of opening up sources of knowledge invaluable to 

 cosmical science, as well as to those only concerned with the 

 planet upon which they dwell. 



When the causes of the secular change are understood 

 there will be no difficulty in providing the navigator with 

 magnetic charts for years in advance, much as the tides can 

 now be tabulated for his use. In the latter case observa- 

 tion has done its work for several frequented ports, in the 

 former case a vast amount remains to be done, and the 

 word that goes forth is still, as Lord Kelvin thrice said 

 on a kindred subject connected with ships' magnetism, 

 " Observe". 



Ettrick W. Creak. 



