148 Mr Christie on the Diurnal Variation 
the needle being suspended by a brass- wire ^i^tli inch * n dia~ 
meter. By them I ascertained the following facts. 
u 1. Commencing with a temperature — 3° Fahrenheit, up 
to a temperature of 127°, as the temperature of the magnets 
increased, their intensity decreased. Owing to the almost total 
absence of snow during the winter, I was unable to reduce 
lower the temperature of the large magnets which I made use of ; 
but, from an experiment I made at the Royal Institution, in 
conjunction with Mr Faraday, in which a small fnagnet, enve- 
loped in lint well moistened with sulphuret of carbon, was placed 
on the edges of a basin containing sulphuric acid, under the 
receiver of an air-pump, I found that the intensity of the mag- 
net increased to the lowest point to which the temperature was 
reduced, and that the intensity decreased on the admission of 
air into the receiver, and consequent increase of temperature in 
the magnet. This is in direct contradiction to the notion which 
has been entertained of destroying the magnetism of the needle 
by the application of intense cold. 
“ 2. With a certain increment of temperature, the decrement 
of intensity is not constant at all temperatures, but increases as 
the temperature increases. 
u 3. From a temperature of about 80°, the intensity decreases 
very rapidly as the temperature increases : so that, if up to this 
temperature, the differences of the decrements are nearly con- 
stant, to ascertain which requires a precision in the experiments 
that perhaps their nature does not admit of, beyond this tempe- 
rature the differences of the decrements also increase. 
“ 4. Beyond the temperature of 100°, a portion of the power 
of the magnet is permanently destroyed. 
46 5. On a change of temperature, the most considerable por- 
tion of the effect on the intensity of the magnet, is produced 
instantaneously ; shewing that the magnetic power resides on 
or very near the surface. This is more particularly observable 
when the temperature of the magnet is increased, little change 
of intensity taking place after the first effect is produced ; on 
the contrary, when the temperature of the magnet is diminished, 
although nearly the whole effect is produced instantly, yet the 
magnet appears to continue to gain a small power for some 
time. 
2 
