OF THE GLOBE. 223 



cold of Lancaster Sound, could experience no hardship under 

 a comparatively milder climate. 



Hitherto we have supposed the two Isothermal Poles to have 

 the same temperature, and to be situated on nearly opposite 

 Meridians ; but this supposition is not rendered necessary by 

 any of the phenomena, and we may obtain a better expression 

 of the temperatures, by placing the Poles at different distan- 

 ces from the Equator, and ascribing to them different intensi- 

 ties. The existence of a cold and a warm meridian, is a proof 

 that there are causes which powerfully influence the annual 

 temperature, independent of the position of the Earth's axis 

 with respect to the Sun ; so that the effects which they pro- 

 duce can have no symmetrical relation to the Pole either in 

 position or intensity. 



The two Northern Poles of the terrestrial magnet, for ex- 

 ample, are situated, the one 4° and the other 20° from the Pole, 

 and they have neither equal intensities, nor opposite positions. 

 Imperfect as the analogy is between the Isothermal and the 

 Magnetic centres, it is yet too important to be passed over 

 without notice. Their local coincidence is sufficiently remark- 

 able, and it would be to overstep the limits of philosophical 

 caution, to maintain that they have no other connection but 

 that of accidental locality. The revolution of the two Magne- 

 tic foci round the Pole, the one in 1740 years, and the other 

 in 860, has been recently deduced by Hansteen from nume- 

 rous observations, and if we had as many measures of the 

 mean temperature, as we have of the variation of the needle, 

 we might determine whether the Isothermal Poles were fixed 

 or moveable. 



The idea of such a motion suggests an explanation of some 

 of the most remarkable revolutions on the surface of the 

 Globe. There is no fact in the Natural History of the Earth 

 better ascertained, than that the climate of the west of Europe 



was 



