120 Mr. Christie on the mutual action of 
small error in the distance, when d is so small as ‘6 or *7 
inch, are considerable ; and to this source we ought perhaps 
to attribute the error in the last observation in Table III. 
being plus instead of minus, as it ought to be from the omis- 
sion of the second and following terms. 
It appears then, that, within the limits of the values of the 
distance c', at which the observations were made, u being 
extremely small, and ^ about 4 °, we may, without any sen- 
sible error, omit the second and following terms in the 
expression for the force, which is thus reduced to the form 
which represents very accurately the several values of «, 
which is the measure of that force, in the experiments. 
I am aware that it may be objected to the method of inves- 
tigation which I have adopted, that the value of $ may not 
be constant for different values of d , nor that of u be constant 
for every point of the ring, behind the portion r >{/, even for 
the same value of c ' : but the variations of these being evi- 
dently within very narrow limits, no sensible error can arise 
from supposing them constant : the perfect coincidence 
between the formula deduced on this supposition, and that 
previously obtained from the experiments, proves clearly that 
this is the case, and that the assumptions which I have made 
are perfectly admissible. 
After the very satisfactory explanation which Mr. Babbage 
and Mr. Herschel have given of the general phasnomena 
observed during rotation, on the principle that time is requi- 
site both for the developement and for the dissipation of 
magnetism,* fully to establish the truth of the principle, 
it remained only to show, that the results obtained from 
Phil. Trans, for 1825. 
