the intensity of magnetic forces ^ &c, $ 
theory, and adopted the simplest, and that which is most 
generally received, viz. that the forces which two magnets 
exert upon one another may be referred to two centres or 
poles in each, near their respective ends ; and that for either 
pole in one of the magnets, one pole of the other magnet is 
urged towards it, and the other from it, by forces varying 
inversely as the squares of their respective distances from 
that pole. Of the correctness of this theory of the action of 
one magnet upon another, the conclusions which I have ob- 
tained have given me no reason to doubt. 
In the observations on the diurnal changes in the positions 
of the points of equilibrium at which the pole of the needle 
was retained by the joint action of two magnets and the ter- 
restrial magnetism, where I noted the changes that took 
place in the temperature of the magnets, to which observa- 
tions I have alluded near the conclusion of my former paper, 
two magnets, as in several of the preceding observations, 
were placed, with their axes in the magnetic meridian, on the 
same horizontal table as the compass, at equal distances from 
the centre of the needle, one towards the north, the other to- 
wards the south, the north pole of each magnet being towards 
the north ; and their distances from the centre were such, that 
the points of equilibrium were nearly 180°, or south, N. 80° 
E. and N. 80° W. To determine here the changes that would 
take place in the situation of these points from clianges in the 
force of the magnets, arising from a variation of their tempe- 
rature, it was first necessary to determine the changes in the 
forces themselves, arising from certain variations of the tem- 
perature of the magnets, by observing the corresponding 
changes in the direction of the needle. 
