of the Terrestrial Magnetic Intensity . 149 
u 6. The effects produced on unpolarised iron by changes of 
temperature, are directly the reverse of those produced on a 
magnet ; an increase of temperature causing an increase in the 
magnetic power of the iron, the limits between which I observed 
being 50° and 100°. That the effect on iron of an increase of 
temperature should be the reverse of that produced on a mag- 
net, is, I think, a strong argument against the hypothesis, that 
the action of iron upon the needle arises from the polarity which 
is communicated to it from the earth. 
“ It may be objected to the method which I have adopted 
for determining the diurnal changes in the terrestrial magnetic 
intensity, that, after the observations have been made, they 
require a correction for temperature, which can only be deter- 
mined by experiments previously made on the magnets and 
needle employed. The same objection may, however, be made 
against the method of determining the intensity by the vibra- 
tions of a needle. As such a correction has not, in the latter 
case, been hitherto applied, the results which have been obtained 
relative either to the diurnal changes of intensity, or the intensi- 
ties in different parts of the earth, by means of observations on 
the vibrations of a needle, will be so far incorrect as the needle 
may happen to have been affected by differences in the tempe- 
rature. The method I have described, however, possesses ad- 
vantages over the other : a very considerable one is, that, what- 
ever effects are produced, may easily be observed with consider- 
able precision, the time required for each observation being not 
more than five minutes ; another is, that, the magnets being im- 
mersed in water, as far as regards them, we may command the 
temperature at which the observations are to be made, and thus 
limit the correction for temperature to a very small quantity ; 
and it possesses another decided advantage, that whatever are 
the effects produced on the needle by atmospheric changes, they 
are, by means of it, rendered immediately visible, and can be 
observed as they occur 
* A series of experiments on the Effects of Temperature on Magnetism, 
by Dr Kupfer, Professor of Natural Philosophy and Chemistry at Kasan, has 
appeared in the 6th volume of Karsten’s Archiv fur Naturliche— Edit. 
