TERRESTRIAL MAGNETISM. 7ll 



opposite direction, which were very rare, can only be looked upon 

 as movements of reaction. 



" The instrument upon which Lieut. Weyprecht placed the 

 greatest expectations, namely, the Earth-current galvanometer, 

 gave no results at all, through the peculiar circumstances in which 

 the explorers were placed. He had expected to be able to con- 

 nect the aurorse with the galvanic Earth currents. But as the ship 

 was lying two-and-a-half German miles from land, he could not 

 put the collecting plates into the ground, but Avas obliged to bury 

 them in the ice. Now, as ice is no conductor, the plates were 

 insulated, and the galvanometer needle was but little affected. 

 Prof. Lament had supplied these excellent instruments also ; the 

 conducting wires were 400 feet long. Later on, Lieut. Weyprecht 

 tried to obtain some results by connecting a collector for atmo- 

 spheric electricity with the multiplier of the galvanometer, but 

 failed, doubtless for the same reason." 



14. Magnetic Survey of the North Polar Regions. 



In the Philosophical Transactions for the year 1872, Part IL, 

 is contained a " Contribution " on this subject from Sir Edward 

 Sabine. It contains the Magnetic Survey of the region from 

 40° N. to the most northern limits for the three magnetic elements, 

 for the epoch from 1842 to 1845. The observations are arranged 

 in eight zones of successive 5° of latitude. 



The observations for Magnetic Force to which, prior to Gauss' 

 improvement, have always been expressed according to some 

 arbitrary scale having reference to the force at a base station, 

 have in this paper been referred to absolute British units. The 

 arbitrary value which used commonly to be adopted for London 

 was 1"372, and for this the value in absolute measure at Kew, 

 viz., 10-28, has been substituted. From 1830 to 1869 the value 

 of Kew has been gradually increasing from 10*27 to 10* 31 units. 



In the American Polar regions there is more than ordinary 

 difficulty in respect to secular change especially of declination; but 

 the facts observed seem to point to a probable reversal in the direc- 

 tion of the secular change at some interval between 1818 and 1860 

 such as has been proved to take place about 1842 at York Fort by 

 the observations of Franklin, Lefroy, and Blakiston. These changes 

 may be connected with the easterly progression in north-eastern 

 Asia, showing the approach of the present Asiatic point of maximum 

 force to the American continent. 



Future researches alone can clear up these difficulties. 



Since the early part of the I7th century the dip on the coasts 

 of Norway and in the Spitzbergen Sea has greatly diminished ; in 

 some cases the recorded observation gave 80° and even 86° in 

 localities where the inclination is noAv \QP less. 



These valuable tables drawn up by Sir Edward Sabiae, and the 

 lines of equal declination, inclination, and magnetic intensity given 

 in the three maps, supply all the information with regard to the 

 absolute values of the magnetic elements in the Polar regions 



