S91 
iron arising from its rotation. 
Here, contrary to what took place when the centre of the 
plate was in the equator, the deviation of the south end of 
the needle is in the direction in which the lower or north edge 
of the plate revolved ; and we may therefore infer, that the 
same would be the case if a needle were suspended freely by 
its centre of gravity, and the plane of the plate were in the 
plane of the secondary to the meridian and equator, its 
centre being in latitude 90° S : which also agrees exactly 
with the directions of the deviation of the horizontal needle, 
due to rotation, in this position of the plate. 
It is evident from these different experiments with the 
dipping needle, that whatever may be the peculiar effects 
produced on the iron by its rotation, the deviations of the 
horizontal needle, due to the rotation, are of the same nature 
as those that would arise by referring the deviations of the 
dipping needle to the horizontal plane. 
Further observations with the horizontal needle. 
Although, in order to point out the particular laws accord- 
ing to which the rotation of the ‘iron causes the needle to 
deviate in particular situations of the plate, and to deduce a 
general law by which the direction of the deviation might in 
all cases be determined from the direction of rotation, I have 
been under the necessity of entering into such a detail of the 
experiments, as has already extended this paper beyond the 
limits to which I wished to confine it, I yet think it may not 
be uninteresting to enquire, how far the adoption of parti- 
cular hypotheses may enable us to account for the several 
phaenomena wi\ich I have observed. 
I have already stated, that I considered that the deviations 
