313 
diurnal variation of the magnetic needle^ ^c. 
again noted, the lamp was again applied to the same point, 
for the same time as before, and a second set of observations 
made, by bringing the several points of the plate to the com¬ 
pass in the order contrary to that which had been previously 
used. By this means, the deviation of the needle corres¬ 
ponding to each position of the plate, and to a temperature of 
the heated point nearly a mean between its temperature at 
commencing and that at concluding the observations, was 
obtained. 
The experiments which I proposed to myself were these : 
to place the plane of the plate vertical, and likewise hori¬ 
zontal ; in the former case both in the plane of the meridian, 
and at right angles to it; to adjust the compass to certain 
positions with regard to its centre and surface, and to observe 
the effects produced on the needle when the heated point on 
the plate had various positions. By this means, I expected 
to be able to determine the nature of the laws which these 
deviations observed in all cases, or the species of polarity 
in the plate which would account for them. Having made 
these observations, I found that, if through the place of heat 
a diameter were drawn, which, for distinction, I call the axis 
of heat, and another at right angles to it, then looking on to 
either side of the plate, with the place of heat downwards, if 
I supposed a south pole in the lower quadrant on the right hand, 
and a north pole in that on the left, the character of the devia¬ 
tions would agree with such polarity of the plate. 
It is not my intention to enter upon any theoretical views 
with regard to the nature of the forces which are the cause 
of thermo-magnetical phasnomena: whether they arise from 
electric currents being excited- in particular directions, and 
MDCCCXXVII. S s 
