TERRESTRIAL MAGNETISM. 119 



preaches the meridian of Paris, the more the rate of decrease 

 appears to slacken, the retardation being in the course of 

 half a century from 5''08 to 3''40. In a memoir which I 

 presented to the Berlin Academy in April 1829, a short 

 time before my Siberian expedition, ( 138 ) I collected and 

 compared the observations made by me, I think I may 

 venture to say, always with equal care. Sabine measured 

 the inclination and the force at the Havannah fully twenty- 

 five years after my observations there, thus giving for that 

 tropical station the variation of two important magnetic 

 elements for a considerable interval. Hansteen (1831) has 

 examined the annual variation of the inclination in either 



hemisphere in a very meritorious and more comprehensive 

 work ( 139 ) than mine. 



While the observations of Sir Edward Belcher in 1838, 

 compared with mine in 1803, indicate considerable changes 

 of inclination along the west coast of America, between 

 Lima, Guayaquil, and Acapulco (vide page 77) (the longer 

 the interval, the greater the value of the results), the secular 

 change in other parts of the Pacific appears to have been re- 

 markably small. At Otaheite, Bayley found, in 1773, 29 43'; 

 Fitz Boy, in 1835, 30 14'; Belcher, in 1840, 30 IT, so 

 that in sixty-seven years the mean annual increase would 

 hardly have been 0'-51( 14 ) In Northern Asia, also, a 

 very careful observer, Mr. Sawelieff, twenty-two years after 

 my visit to those regions, found on a journey which he 

 made from Kasan to the shores of the Caspian, that very 

 unequal changes had taken place in the inclination on the 

 north and south sides of the parallel of 50 of geographical 

 latitude. ( 141 ) 



