14 Mr Harris on Magnetic Intensity by the 
cuo in small ares, 100 vibrations in 11’ 56”, 6, after exposure for 
about half an hour to a cold of about 5° of Fahrenheit’s scale ; 
it made under similar circumstances 100 vibrations in 11’ 65” ; 
whilst in other cases, similar bars, after being freely exposed to a 
range of temperature from 0° to 212°, appeared to remain inva- 
riable, in respect of certain ranges of temperature taken between 
these points. These results have received some confirmation 
since the notice of my paper on this subject, read at the Meeting 
of the British Association in June last, as appears in a letter to 
Dr Brewsrer from Professor Kurrrer of the Imperial Academy 
of St Petersburgh, printed in the London and Edinburgh Jour- 
nal of Science for August 1832. The coincidence between Mr 
Kurrrer’s results and my own is not a little remarkable. I 
have been hence led to hope, that the effects of heat in disturb- 
ing the tension of a vibrating needle, may in certain cases be con- 
fined to differences of temperature, without the limits of that to 
which the needle has been previously exposed. I desire, however, 
to evince no greater confidence in this opinion, than the results 
of the experiments above alluded to seem to warrant. Mr 
Curistie’s profound and interesting researches in this depart- 
ment of science have undoubted claims to our confidence; and 
we must therefore endeavour, by further investigation, to discover 
the source of the apparent anomalies which occasionally present 
themselves. It may be fairly observed, at least, that whilst such 
questions as these, and others of no less consequence, remain in 
any degree doubtful, it is quite impossible to place confidence in 
results pretending to detect small periodical variations in the ter- 
restrial intensity, which variations, if such exist, may cause diffe- 
rences in time, certainly much smaller than might alone arise from 
either of the foregoing causes. 
25. Beside the changes of tension induced in a bar by heat, 
we have to consider those which may happen from the manner 
of preserving the magnets themselves, such as occasional contact 
with each other, or with masses of iron. The usual method of 
