495 
and magnetic rotations. 
If N represent the north pole of a magnet, Plate XIX, 
fig. 4, placed above an indefinite plate AB, of iron or any 
substance susceptible of magnetism, then the point S imme- 
diately under N will become a south pole from induced mag- 
netism : but the two poles will attract each other, and if 
they are prevented from moving directly towards each other, 
motion cannot arise in any other direction. The point S 
immediately under N will possess the strongest south pola- 
rity, but other adjacent points will also acquire the same pro- 
perty in a smaller degree : if an ordinate S K be erected at S, 
and if at every other point in the line AB other ordinates be 
raised, each proportional to the intensity of the induced mag- 
netism at that point, a curve EKF will be formed, which 
will represent the magnetic force of the plate, and at equal 
distances CS, SD, on each side of the point S the ordinates 
EC and FD will be equal. 
If the plate is now supposed to be moved in the direction 
AB, and if the time in which it acquires or gives up any 
portion of magnetism be not instantaneous, then the ordi- 
nates which represent the magnetic intensities at equal dis- 
tances from the middle point S will not be equal : for the 
point D has, in consequence of the motion of the plate, just 
passed through a point S, considerably nearer to the source 
of magnetism, at which point its magnetic intensity was ex- 
pressed by S K. As it is supposed not to part immediately 
with its acquired magnetism, some portion will remain when 
it reaches the point D : therefore the ordinate D G, at this 
point, will be greater than it is when the plate is at rest ; 
consequently the curve EKG, expressing the magnetic 
force when the plate is in motion, will, on the side towards 
