210 



Prof. W. A. Norton on Terrestrial Magnetism.. 



The value to be assigned 



level of the sea we have 31° nearly. 



to t would seem to be the mean of the temperatures of the two 



cold 



According to 



poles. 

 17°'2: the mean of which is 



Berghaus, these are 



19° -7 and 



18*4. 

 -18 



The most probable 

 The folio wing table 



values of t and t are then 31°. and - 



was calculated with these values, taking n — j ; or by the formula 



3 



8 



T = 49°(sin p (Jsin^ / ) 



18 



(9.) 



It will be seen that the difference between the computed and 

 observed temperatures in no case exceeds 1°, and is generally 

 much less. Thus the same values of <5 and 3' give by this for- 

 mula the temperature of a place, and by formula (6), derived 

 from this by differentiation, the declination of the 

 needle. 



magnetic 



Table III. 



derhn, 



M ;co\v, 



itretensk, 

 Tschei noljes 

 Crga, 

 The Azores, 



M. Anna <1 Temp 

 computed observed 



9°-3 

 4 i 



3 

 -6 



6 

 i5 



•5 



•4 

 ■i 



•6; 



8 



4 

 3 



-7 

 6 



16 



C. 



Place. 





M. Annual Temp. 



\ 



Havana, 



Washington, 

 •o-f-o *5j8t. Louis, 



Lon.93°W.,Lat 



Lon.93°W.,Lat 



Lon.!«°W.,Lat. 



-o 



6 



2 



4 



50° 

 55° 



60° 



computed 



ii 8 



12 6 



2 -5 



-2 -5 



-8 -o 



observed! 



. Diff. 



On examining Table I, it will be perceived that, leaving out 

 of view the cases of Havana, Jakutsk, and Tschernoljes, the polar 

 distance of the fictitious American pole varies between 23° and 

 15°, and its longitude between 65° and 95°. In Western Europe 

 its longitude is from 65° to 72° ; in Asia from 80° to 95° ; in 

 the eastern and northern parts of North America from 85° to 90°, 

 and in the western part from 70° to 85°. The smaller polar 

 distances obtain only on this continent. As to the Asiatic pole; 

 on the meridian of Paris, over the Atlantic Ocean, and through- 

 out this continent, it is to be taken 160° east of the meridian ot 

 the place, and at the distance of 25° from the geographical pole- 

 In passing over Europe and Asia, the Asiatic pole moves west- 

 wardly, and at the same time approaches the geographical pole- 

 At from 100° to 120° east longitude, it falls to the west of the 



to 15 



pol 



tical 



\ As we approach either magnetic pole, the hypotheti; 

 pole of maximum cold approaches this pole and the true position 

 of the cold pole. A change either in longitude or latitude alters 

 more or less the ideal positions of the cold poles. The change* 

 of longitude and latitude of the Asiatic pole are about twice a? 

 great as those of the longitude and latitude of the American P o1 ^ 

 It appears from Tables II and III, that in using Brewster 

 formula for the calculation of thp moan tpmnArntnre of a ] 



may 



ace, 

 ile 



po 



les 



