THE 



AMERICAN 



JOURNAL OP SCIENCE AND AETS. 



[SECOND SERIES.] 



Art. I. — On Terrestrial Magnetism 



College. 



Mathematics 



I propose in the present article to show that, adopting certain 

 fundamental conceptions with respect to the terrestrial magnetic 

 forces, the magnetic may be deduced from the thermal elements 

 of the earth. The first investigations tending to establish the ex- 

 istence of a physical connection between the heat and magnetism 

 of the earth, seem to have been made by Sir David Brewster. 

 In 1820 he announced the " discovery of two poles of maximum 

 cold on opposite sides of the north pole of the earth,' 7 and in the 

 vicinity of the two magnetic poles ; and maintained the proba- 

 bility of some physical connection between the poles of maxi- 

 mum cold, and the magnetic poles. He also proved " that the 

 circle of maximum heat, like the magnetic equator, did not coin- 

 cide with the equinoctial line ; that the isothermal lines and the 

 lines of equal magnetic intensity, had the same general form 

 surrounding and enclosing the magnetic poles and those of max- 

 imum cold ; and that, by the same formula, mutatis mutandis, we 

 could calculate the temperature and the magnetic intensity of any 

 point of the globe." This subject has since been studied by sev- 

 eral philosophers ; and particularly by Captain Duperrey, and M. 

 Kupffer of Kasan. The original memoirs of these authors I 

 have not seen. The following is the substance of the account 

 which Sir David Brewster gives of their investigations. In the 

 years 1822-1825, Captain Duperrey made an extended system of 

 magnetic observations in the vicinity of the equator, by which 



Second Series, Vol. IV, No. 10.— July, 1847. 1 



