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diurnal variation of the magnetic needle^ &c. 
copper and bismuth, since these situations of the needle 
would correspond to those of a needle placed succes¬ 
sively in the higher regions of the atmosphere, and on the 
surface of the earth. As the character of the deviations is 
the same in the two cases, it would follow, that the course of 
the daily changes in the direction of the needle would be the 
same at the level of the sea, and at the summit of the highest 
mountain, although the extent of those changes might be 
slightly different. At the time of making these experiments, 
and when I had drawn this conclusion, I was not aware that 
Lieut. Foster had made any observations at Port Bowen, 
with the view of comparing the changes which take place in 
such cases ; but, previously to his sailing for Spitzbergen, he 
informed me, that at Port Bowen he had found them to be 
simultaneous. 
I am perfectly aware that it would have been more satisfac¬ 
tory, had 1 drawn my conclusions from experiments on sub¬ 
stances in contact more precisely in the manner of the earth 
and the atmosphere; that is, for example, from experiments 
on a copper shell filled with bismuth. This 1 proposed doing, 
and for the purpose had a six-inch copper shell cast, into which, 
after having it cleaned and soldered on its inner surface, I cast 
bismuth to fill it. In consequence however of inequalities in 
the thickness of the copper, and possibly from imperfect con¬ 
tact in some parts, the results, when different points had been 
heated, were not, in all cases, of such an uniform character as 
to enable me to determine the general magnetical phenomena 
that would ensue from applying heat to any part of the sphere. 
This being the case, I shall detail none of these experiments. 
As however one effect, which was invariably produced to 
