100 Terrestrial Magnetism. 



IX. — Terrestrial Ma 



Penn. 



In the 22d volume of this Journal 1 suggested the idea^ that 

 the magnetic poles coincided with the coldest points in the north- 

 ern hemisphere, but did not assign the grounds for such a con- 

 clusion. 



In 1837, Dr. Brewster published his Treatise on Magnetism at 

 Edinburgh, originally prepared for the Encyclopedia Britanica, 

 which contains very full details of the latest researches on that 

 subject. 



In the 42d page of this Treatise it is stated, ^^ the discovery of 

 two poles of maximum cold on opposite sides of the north pole of 

 the earth, which was announced by Sir David Brewster in 1820, 



led him and other authors to the opinion, that there might be 



some connection between the magnetic poles, and those of maxi- 

 mum cold." The opinion advanced by Dr, Brewster, " that there 

 are two poles of greatest cold in the northern hemisphere," it ap- 

 pears, was published in the 9th volume of the Edinburgh Trans- 

 actions of 1S21, and Dr. Dalton in remarking on it, considers it as 

 a probable supposition^ and Mr. Kupffer in a memoir read in 1829 

 to the Russian Academy, explicitely adopts the opinion. 



Of all this I knew nothing when I wrote the letter above re- 

 ferred to in 1832, nor until I met with Dr. Brewster's Treastise 

 published in 1837; but drew the inferences therein stated, from 

 the views I entertained of the nature of light and heat,* and from 

 observing a certain correspondence of climate at similar distances 

 from the magnetic poles. 



I regard light and heat in the common acceptation of these words, 

 as not only material in their nature, but as compounds of other 

 simple elements, and suppose the magnetic fluids to be two of 

 those simple substances which enter into their constitution. 



From the refined nature of light and heat, we cannot subject 

 them to experiment like other forms of matter, and the difficulty 

 would necessarily be increased, if we have to do with the simple 

 elements of which they are here supposed to be compounded. 



That matter exists in such states of refined minuteness of 



« 



atomsj as to be imperceptible to such senses as we possess, is 



ciple. 



By the word " heat" I always mean sensible keatj and not the unknown prin- 



