58 Mr. Christie on the effects of temperature on 
intensity increased until about six o'clock in the afternoon, 
after which time it appears to have decreased during the 
these phoenomena. The circumstance of the situation of the magnetic pole in what 
appears to be, independent of elevation, the coldest region of the globe, supported 
as it is by the fact of a diminution of temperature causing an increase of magnetic 
intensity, would lead us to infer, that the effect produced by the sun is principally 
to be attributed to the heat developed by it ; but should any periodical effects, 
corresponding to the time of the sun’s rotation about its axis, be observable in the 
diurnal variation, we must suppose that the sun, like the earth, is endued with 
magnetism, and look for a cause of this magnetism, common to all the planets. 
Being engaged more than two years ago in making some experiments on the effects 
produced on the needle by unpolarized iron, I discovered that a peculiar polarity 
was imparted to the iron by simply making it revolve about an axis ; and this 
naturally suggested the question to me, whether the magnetism of the earth, and 
consequently, that of the other planets and the sun, might not be owing to their 
rotation? From the effects which I have observed to be produced on iron by its 
rotation, it appears probable, if the magnetism of these bodies be not caused by 
their rotation, that at least the effects will be modified by, and, to a certain extent, 
dependent on such rotation. Since first observing the fact, that simple rotation 
will cause a peculiar polarity, if I may be allowed the expression, in iron, I have 
made a great variety of experiments on the subject, which have enabled me to trace 
the laws according to which this polarity in the iron affects a magnetic needle, 
independently of the effect (produced by the mass. It would lead me to too great 
a length here to state the several effects that are produced by the rotation of iron, 
or the laws which govern them ; but I will briefly mention one. Let us imagine a 
plane to pass through the centre of an horizontal needle, at right angles to the 
meridian, and making an angle with the horizon equal to the dip ; then, if the 
plane of a circular plate of iron coincide with this plane, and the plate be fixed on 
an axis passing through its centre at right angles to its plane, so that it can be 
made to revolve in its own plane, the direction of the needle will be different, 
according as the several points of the plate are brought into any particular position 
by making it revolve in one direction or the opposite, excepting in four positions 
of the centre of the plate. If the centre of the plate be successively placed to the 
east or west of the centre of the needle in the same horizontal line, and over the 
needle in the plane of its meridian, then the deviation of the needle due to the 
rotation of the plate will be in contrary directions in the two cases, the plate 
revolving in the same direction in both. These and other peculiar effects arise 
