ATMOSPHEROLOGY. — EFFECTS OF COLD. 333 



ther the attractive nor directive power of the mag- 

 net, appears to suffer any diminution by an increase 

 of cold. A magnet which, with difficulty, support- 

 ed a weight of seven pounds in my cabin, where the 

 temperature was 50°, on being removed into the air, 

 where a cold of 8° prevailed, also supported the 

 same, and after some interval one pound more ; but 

 on another pound being added, the weight fell off, 

 and it would then only carry seven pounds as be- 

 fore. Hence, the attractive property of the magnet 

 could not be said to be diminished, and scarcely to 

 be increased, by a reduction of temperature amount- 

 ing to 42°. A theodolite needle, 5.55 inches in length, 

 when made to oscillate horizontally in the cabin, 

 performed ten vibrations in sixty seconds, and then 

 ceased. On the deck, it oscillated five times in 

 thirty seconds, and then ceased. Thus, the time re- 

 quired for performing a vibration, was the same 

 both in a high and in a low temperature ; conse- 

 quently, the directive force is unaffected by changes 

 in temperature ; but the number of vibrations per- 

 formed by the needle, though equally deflected from 

 the magnetic meridian when set in motion, was 

 much fewer in a cold situation, than it was in a 

 warm one. Hence, though the magnetic influence, 

 both as to its attractive and directive property, be 

 fully as great in low as in high temperatures, yet 

 there appears to be an increase of friction, or an in- 

 troduction of some unknown principle, which occa- 



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