152 TERRESTRIAL MAGNETISM. 



declination which increases, in penetrating towards the 

 interior of the oval. In the Pacific oval we only know 

 at present declinations of from 8 to 5. May there 

 be, more in the interior, another line of no declination 

 enclosing a space of westerly declination ? 



The curves of no declination, like all the magnetic 

 lines, have each their own proper history, although . it 

 can only in any case be very imperfectly traced back 

 beyond two centuries. We possess, indeed, detached 

 materials of an earlier date, going back even to the 

 14th and 15th centuries. Hansteen has here also the 

 great merit of having assembled and compared the data 

 with great judgment. It would appear as if the north 

 magnetic pole were moving from west to east, and the 

 south magnetic pole from east to west : but we know 

 from exact observations, that different portions of the 

 isogonic curves advance at very unequal rates of pro- 

 gression, that where they were once parallel, they are 

 now no longer soy and that adjoining regions, over 

 which decimations of opposite denominations prevail, 

 enlarge and contract in very different directions. The 

 lines of no declination in Western Asia and the Atlantic 

 Ocean advance from east to west. The former (or West 

 Asiatic) passed through Tobolsk in about 1716 ; Catha- 

 rinenburg (in Chappe's time) in 1761 ; and between 

 Osablikowo and Doskino (not far from Nishnei Nov- 

 gorod) in 1829; so that in 113 years it had advanced 

 24 f towards the west. If the line of no declination of 

 the Azores, determined by Columbus on the 13th of 

 September 1492, was the same line which, according to 

 the observations of Davis and Keeling, passed in 1607 

 through the Cape of Grood Hope, ( 199 ) and the same 



