326 Mr. Christie’s theory of the 
them to be the points of greatest intensity. Throughout the 
observations, however, a certain degree of irregularity was 
manifested when the heated point was that nearest to the 
compass. This, supposing the action to be produced by 
currents excited in the plate, would arise from the much 
greater energy of these currents in the immediate neigh- 
bourhood of the heated point, and likewise from their being 
more influenced by variations in the temperature of that 
point there, than elsewhere. And it is to be observed, that 
although I have in a general manner referred the action of 
the whole plate to four poles, in certain positions, yet I by no 
means suppose, that the forces acting upon the needle tend 
to points absolutely fixed, whatever may be the position of 
the compass : and, indeed, I have rather adopted the term, 
pole, to illustrate, in a general manner, the nature of the 
effects, than as supposing that the action which takes place 
between the plate and the needle can, in all cases, particularly 
in the immediate vicinity of the heated point, be precisely re- 
presented by that which would take place between the poles 
of two magnets. 
It appears, then, from all these observations, that, when 
heat was applied to a point in the copper ring, the characters 
of the deviations of the needle, and generally also their ex- 
tent nearly, were such as would arise from a polarising of 
the plate in lines nearly at right angles to the axis of heat , 
and cutting that axis between the centre and the place of 
heat, near each surface, contrary poles being opposite to each 
other in the two surfaces. We may therefore, I think, infer, 
that, if magnetic phaenomena are manifested by heat being 
applied to the joint of two substances, united in any of the 
