354 
Mr. Christie’s theory, &c. 
I have mentioned that, owing to the want of uniformity in 
the thickness of the ccpper, and possibly likewise in the 
contact of the two metals, some other results which I obtained 
with this sphere were not of the same uniform character. I 
have however not yet been able to make such alterations in 
the apparatus as shall remedy this defect. If, with an appa¬ 
ratus similar to that which I employed, but of much larger 
dimensions, and in which the copper sphere should be of 
uniform thickness, and the contact of the two metals perfect 
throughout, means were adopted by which the distribution 
of heat should nearly resemble that on the earth, and that 
observations were made with such adjustments of the instru¬ 
ment, that the positions of the needle should correspond to 
those of a horizontal and of a dipping needle on different 
parts of the earth’s surface, I consider that much light might 
probably be thrown on the various phenomena of terrestrial 
magnetism. 
S. H. CHRISTIE. 
Royal Military Academy, 
26th May, 1827, 
