ACTION OF MAGNETS ON COPPER AND GOOD CONDUCTORS. 
35 
the experiment, from which the magnetism does not move it, the equatorial and 
the axial positions. When the bar is nearly midway between these, it is usually 
most strongly affected by the first action of the magnet, but the position of most 
effect varies with the form and dimensions of the magnetic poles and of the bar. 
2314. If the centre of suspension of the bar be in the axial line, but near to one of 
the poles, these movements occur well, and are clear and distinct in their direction: 
if it be in the equatorial line, but on one side of the axial line, they are modified, but 
in a manner which will easily be understood hereafter. 
2315. Having thus stated the effect of the supervention of the magnetic force, let 
us now remark what occurs at the moment of its cessation ; for during its continu- 
ance there is no change. If, then, after the magnetism has been sustained for two or 
three seconds, the electric current be stopped, there is instantly a strong action on 
the bar, which has the appearance of a revulsion (for the bar returns upon the 
course which it took for a moment when the electric contact was made), but with 
such force, that whereas the advance might be perhaps 15° or 20°, the revulsion 
will cause the bar occasionally to move through two or three revolutions. 
2316. Heavy glass or bismuth presents no such phenomena as this. 
2317- If, whilst the bar is revolving from revulsion the electric current at the 
magnet be renewed, the bar instantly stops with the former appearances and results 
(2310.), and then upon removing the magnetic force is affected again, and, of course, 
now in a contrary direction to the former revulsion. 
2318. When the bar is caught by the magnetic force in the axial or equatorial 
position, there is no revulsion. When inclined to these positions there is ; and the 
places most powerful in this respect appear to be those most favourable to the first 
brief advance (2313.). If the bar be in a position at which strong revulsion would 
occur, and whilst the magnetism is continued be moved by hand into the equatorial 
or axial position, then on taking off the magnetic force there is no revulsion. 
2319. If the continuance of the electric current and consequently of the magnetism 
be for a moment only, the revulsion is very little, and the shorter the continuance of 
the magnetic force the less is the revulsion. If the magnetic force be continued for 
two or three seconds and then interrupted and instantly renewed, the bar is loosened 
and caught again by the power before it sensibly changes its place ; and now it may 
be observed that it does not advance on the renewal of the force as it would have done 
had it been acted on by a first contact in that place (2310.) ; i. e. if the bar be in a 
certain place inclined to the axial position, the first supervention of the magnetic 
power causes it to advance towards the axial position ; but the bar being in the same 
place and the magnetic power suspended and instantly renewed, the second super- 
vention of force does not move the bar as the first did. 
2320. When the copper bar is immersed in water, alcohol, or even mercury, the 
same effects take place as in the air, but the movements are, of course, not to the 
same extent. 
