THE BEARINGS OF MAGNETIC OBSERVATIONS. 85 



three magnetic elements became a necessity in solving the 

 problems which the magnetism of different iron ships 

 presented. 



With Gauss's invention of the absolute horizontal force 

 magnetometer in 1833, many hitherto unknown move- 

 ments of the magnetic needle of the highest interest were 

 discovered, which with the coarser instruments previously 

 in use lay concealed. This discovery gave the desired 

 impetus to the scientific men of that epoch, and the period 

 included in the years 1835-45 was "a time of unparalleled 

 activity in the extension of systematic and accurate mag- 

 netical observations over the earth's surface ". 



Whilst most of the continental nations joined in this 

 movement, the principal share in the work was divided 

 between Germany, Russia, and England in Europe, and the 

 United States in America. But before the splendid series 

 of simultaneous observations made on the continent, and 

 four British colonial observatories were organised, Gauss 

 in 1839 published his general theory of Terrestrial Magnetism 

 coupled with a series of charts of the three magnetic elements 

 for the whole world, based upon observations made at 

 ninety-two selected stations distributed over the earth's 

 surface ; and it may be remarked that Gauss's charts not 

 only gave results in fair accordance with observation in 

 explored regions, but also as afterwards proved in Antarctic 

 latitudes hitherto unvisited by man. 



The proof came in the years 1839-43, when Ross's 

 Antarctic voyage of exploration was carried out in the 

 interests of terrestrial magnetism. Besides the importance 

 of a knowledge of the general distribution of the magnetic 

 elements in those regions, one great aim of this expedition 

 was to reach the south magnetic pole. This was found to 

 be impossible, but sufficient data were collected to give its 

 approximate position. Whilst this Antarctic magnetic 

 survey was being completed, that of British North 

 America was also undertaken with the result of the deter- 

 mination of the locality of one of the foci of greatest 

 intensity in the northern hemisphere. 



The results of these surveys formed, as will be well 



