EXPLICATION OF ARAGO’S MAGNETIC PHENOMENA. 
157 
currents of positive electricity set from the central parts in the general di- 
rection of the radii by the pole to the parts of the circumference a on the 
other side of that pole (99. 119.), and are therefore exactly in the same rela- 
tion to it as the current in the wire (P N, fig. 26.) and therefore the pole in the 
same manner moves to the right hand. 
122. If the rotation of the disc be reversed, the electric currents are re- 
versed (91.), and the pole therefore moves to the left hand. If the contrary 
pole be employed, the effects are the same, i. e. in the same direction, because 
currents of electricity, the reverse of those described, are produced, and by 
reversing both poles and currents, the visible effects remain unchanged. In 
whatever position the magnetic axis be placed, provided the same pole be 
applied to the same side of the plate, the electric current produced is in the 
same direction, in consistency with the law already stated (114, &c.) ; and thus 
every circumstance regarding the direction of the motion may be explained. 
123. These currents are discharged or return in the parts of the plate on 
each side of and more distant from the place of the pole, where, of course, the 
magnetic induction is weaker: and when the collecters are applied, and a cur- 
rent of electricity is carried away to the galvanometer, the deflection there is 
merely a repetition, by the same current or part of it, of the effect of rotation 
in the magnet over the plate itself. 
124. It is under the point of view just put forth that I have ventured to say 
it is not necessary that the plate should acquire and lose its state in a finite 
time (120.) ; for if it were possible for the current .to be fully developed the 
instant before it arrived at its state of nearest approximation to the vertical 
pole of the magnet, instead of opposite to or a little beyond it, still the relative 
motion of the pole and plate would be the same, the resulting force being tan- 
gential instead of direct. 
125. But it is possible (though not necessary for the rotation) that time 
may be required for the development of the maximum current in the plate, in 
which case the resultant of all the forces would be in advance of the magnet 
when the plate is rotated, or in the rear of the magnet when the latter is ro- 
tated, and many of the effects with pure electro-magnetic poles tend to prove 
this is the case. Then, the tangential force may be resolved into two others, 
one parallel to the plane of rotation, and the other perpendicular to it ; the 
