114 ' THIRD REPORT — 1833. 



application of heat, the phaenomena corresponding to magnetic 

 polarization in a particular direction with reference to the place 

 of greatest heat*. From these experiments I drew the con- 

 clusion that one part of the earth, with the atmosphere, being 

 more heated than another, two magnetic poles, or rather elec- 

 tric currents producing effects referrible to such poles, would 

 be formed on each side of the equator, poles of difterent names 

 being opposed to each other on the contrary sides of the equa- 

 tor; and that different points in the earth's equator becoming 

 successively those of greatest heat, these poles would be carried 

 round the axis of the earth, and would necessarily cause a de- 

 viation in the horizontal needle f. On comparing experimentally 

 the effects that would result from the revolution of such poles 

 with the diurnal deviations at London, as observed by Canton 

 and Beaufoy, also with those observed by Lieut. Hood at Fort 

 Enterprise, and finally with the late Captain Foster's at Port 

 Bowen, I found a close agreement in all cases in the general 

 character of the pliEenomena, and that the times of the maxima 

 east and west did not differ greatly in the several cases. The 

 double oscillation of the needle, to which I have referred in 

 Canton's and Beaufoy's observations, clearly resulted from this 

 view of the subject. Some of the experiments to which I have 

 referred showed that when heat was applied to a globe, the 

 electric currents excited were such, that on contrary sides of 

 the equator the deviations of the end of the needle of the 

 same name as the latitude were at the same time always in the 

 same direction, either both towards east or both towards west. 

 No observations having at that time been made on the diurnal 

 variation of the needle in a high southern latitude, I considered 

 *' that the agreement of the theoretical results with such ob- 

 servations would be almost decisive of the correctness of the 

 theory." Captain Foster's observations at Cape Horn, South 

 Shetland, and the Cape of Good Hope, show most decidedly 

 that in the southern hemisphere the diurnal deviations of the 

 south end of the needle correspond very precisely with those of 

 the north end in the northern hemisphere ; and most fully bear 

 me out in the view which I had taken. These valuable obser- 

 vations have been placed in my hands by His Royal Highness 

 the President, and the Council of the Royal Society, and I in- 

 tend, when I have sufficient leisure, rigidly to compare them, 

 and likewise those to which I have already referred in the 

 northern hemisphere, with the diurnal deviations that would 



• "Theory of the Diurnal Variation of the Magnetic Needle," Philosoj)Mcal 

 Tramactions, 1827, pp. 321, 326. 

 I- Ibid. pp. 327, 328. 



