402 
Mr. Christie on the magnetism of 
tions : and although the results of the theory agree in gene- 
ral very nearly with the observations, and the differences 
in the other values of are not greater than might possibly 
be attributed to errors of adjustment or observation, how- 
ever little I may be disposed to admit the existence of errors 
to this extent, yet the uniform manner in which these values 
decrease, indicates that the effects are not produced in pre- 
cisely the manner we have supposed. In one point our 
theory is unquestionably at variance with the actual circum- 
stances of the case ; for we have supposed that no partial 
magnetism exists in the iron, or that every part of it taken 
separately would equally affect the needle. It is, I believe, 
scarcely possible to procure iron that shall possess this uni- 
formity of action, and it is evident that this was not the case 
with the plate of iron which I made use of. This species of 
polarity in iron is of so variable a nature, since by an acci- 
dental blow it will be transferred from one point to another, 
that it does not appear possible in any manner to submit its 
effects to calculation. It was to prevent these effects embar- 
rassing the results, that I took the mean of twelve observa- 
tions for each position of the plate; still it is possible that 
some of the differences between the observations and the 
results of the theory may have arisen from this cause. 
As the results of the hypothesis which I have advanced do 
not precisely agree with the observations, it will be proper 
to enquire whether we shall obtain a more perfect agreement 
by means of the hypothesis commonly assumed, in order to 
account for the effects produced on the needle by a mass of 
soft iron, viz. that the upper part of every mass of iron acts 
as a north pole and the lower part as a south pole. Let us 
