314 Mr G. A. Rowell on the 



Now, if the point of greatest cold were at the terrestrial 

 pole, and the temperature and evaporation increased regu- 

 larly from thence to the equator, the electricity would pass 

 off from the pole towards the warmer parts of the earth, 

 directly in the lines of longitude, and there would be no de- 

 clination of the needle except that caused by the greater 

 evaporation, where the sun may be above the horizon. But 

 as the poles of cold are at a distance from the terrestrial 

 pole, as there is more electricity received at these parts than 

 in others in the same latitudes, the electricity cannot all pass 

 off in the lines of longitude, but must diverge eastward and 

 westward of them, to gain its equilibrium in passing off to- 

 wards the more negative parts of the earth, and thus cause 

 the declination of the needle as the currents of electricity 

 from the frigid to the tropical regions in every meridian 

 must, in some degree, be affected by the divergences of the 

 currents from the magnetic poles. As I consider the poles 

 of cold and magnetic poles identical, I shall use the terms as 

 synonymous. 



The lines of equal intensity of magnetism by no means 

 correspond with the parallels of latitude. If we trace the 

 line 1.5, it has its highest northern limit, i. e. 73° north lati- 

 tude, at about 10° east longitude. To the westward it de- 

 scends through Iceland, passes west of the Azores, and 

 reaches its lowest latitude, 23° north, in the Gulf of Mexico ; 

 it then rises again, and about 20° west of Behring's Strait 

 has its second highest latitude 53° ; it declines again to 41" 

 in the meridian of the Asiatic pole, from whence it rises 

 again to its highest northern limit. The course of this line 

 shews the great intensity of the American pole as compared 

 with the Asiatic. The declination of the needle also shews 

 the different effects of the two poles, as the declination ap- 

 parently caused by the Asiatic pole does not extend over 

 more than about 100° of longitude ; whilst the declination of 

 the needle over the remaining 260° seems to be affected in 

 some measure by the American pole. This difference in the 

 intensity of the influence of the poles may arise from the 

 American pole being the coldest, or from the air forming 

 the upper current to that pole, being more loaded with va- 



