iron arising from its rotation. 
411 
On comparing together the several values of and 
also of contained in this table, there can, I think, be no 
doubt that if the formulae (9) and (10), on which these values 
depend, be not absolutely correct, they will, at least, give in 
all cases, as close approximations to the values of and 
that would be obtained by actual observation, as the nature 
of the case appears to admit of. It is very possible that 
some modification in the theory which I have examined might 
lead to the omission of the terms 2 cos. x — 1 -h . s sin. 2 x 
in the formulae (5) and (6) ; and should this be the case, that 
the formulse (9) and (10) were to be derived from the theory 
so modified, it would, I think, be a very strong presumption in 
favour of the truth of such a theory. 
Since it appears from all the observations which I have 
detailed, that the direction of the magnetic polarity, which 
iron acquires by rotation about an axis, whether it be at right 
angles to the line of the dip, as would follow from the theory 
which I have investigated, or not, has always reference to 
the direction of the terrestrial magnetic forces, we must infer 
that this magnetism is communicated to it from the earth. It 
does not therefore appear from this, that a body can become 
])olarised by rotation alone, independently of the action of 
another body : so that if from these experiments we might 
be led to attribute the magnetic polarity of the earth to its 
rotation, we must at the same time suppose a source from 
which magnetic influence is derived. Is it not then possible 
that the sun may be the centre of such influence, as well as 
the source of light and heat, and that by their rotation, the 
MDCCCXXV. 3 H 
