VI 



subject. This work was only preparatory to his great object. He wished 

 to make a mathematical analysis of all the observations in the light of 

 Eider's theory of magnets ; and he strove to test Halley's speculations 

 as to the existence of four maguetic poles in the earth, and to give a 

 satisfactory answer to the critical problem presented by the Danish 

 Academy of Sciences. 



His Declination chart for 1787 was more accurate and full than similar 

 charts already published by Halley, by Mountain and Dodson, and by 

 Churchman. 



He decided that there were two magnetic poles in the northern and 

 two in the southern hemisphere ; and he inferred from the secular changes 

 in these lines that the northern magnetic poles were moving obliquely 

 towards the east, and those in the south towards the west. He calcu- 

 lated approximately the period of complete revolution for each pole, and 

 called attention to the following coincidence, namely, that the shortest 

 time in which all the poles will return to the same relative position 

 agreed closely with the period of revolution in the precession of the 

 equinoxes. 



By the liberality of the Norwegian Government he was enabled to go 

 to Siberia, in company with Due and Erman, to search for the ideal 

 point of the Asiatic Pole of Magnetism. They started from Berlin on 

 the 25th of April, 1828, and reached Kiachta and Irkoutsk. The Russian 

 Government offered every facility for the success of the expedition, and 

 the results were important. Ten magnetic observatories were established 

 in the Russian Empire by the recommendation of Humboldt, and great 

 results were obtained by Gauss, Sabine, Lamont, and others from th* 

 materials collected by Hansteen and Erman. Hansteen ascertained 

 beyond dispute the existence of a magnetic pole in Siberia supplementary 

 to that in British America, and also the biaxial character of the earth's 

 magnetism. 



Hansteen's elaborate treatise on Terrestrial Magnetism contains a dis- 

 cussion on the Isoclinic and Isodynamic lines, and on those of Declina- 

 tion. His Magnetic Atlas contained maps of dip and intensity. 



These observations have of course up to the present time been added 

 to in so far as the increased number of observations in the Arctic and 

 Antarctic regions, in the United States of America, and at the numerous 

 magnetic observatories have supplied more accurate and abundant data. 

 The work has been described as a monument of industry, learning, and 

 mathematical skill. 



Soon after his Siberian expedition Hansteen prevailed upon the Nor- 

 wegian Government to erect in Christiania an observatory fitted up for 

 Magnetic Observations, and he was appointed Director of this Institution. 



Hansteen reaffirmed the Decennial period as the result of 25 years of 

 observation in Christiania, changing it, however, from 10 years to 11*33 ; 

 and the coincidence between this period and that of the solar spots has 



