87 
of Edinburgh , Session 1875 - 76 . 
absolute symmetry in the arrangements. This rotated the glass 
rod slightly, and produced a little confusion. But beyond this 
there was an undoubted effect, for the nature of the deflection was 
found to depend upon the polarity of the two poles, the effect being 
different according as the upper pole was a north or a south one. 
I was sometimes able, simply by timing the reversals of the com- 
mutator, to get up a very large rotation-swing, and by the same 
means I was able to stop the rotation swinging. 
I delayed the publication of these experiments with the view 
of establishing more certain results. But much time has elapsed, 
and I have still been unable to find time for this. Hence, I am 
unwilling any longer to withhold their publication. I will now 
give the experiments in detail, and will conclude by collecting the 
general results. 
Description of the Apparatus. 
A rod of glass was suspended by a strand of silk fibres attached 
to one end. This was supported on a stone imbedded in the wall 
of the laboratory. The rest of the apparatus was on a separate 
stand. A horse-shoe electro-magnet was placed so that the poles 
were vertically over each other, and as nearly above and below the 
axis of the glass rod as possible. Thus the axis of the glass rod 
lay along the lines of magnetic force. The electro-magnet was 
connected through a commutator with a battery of Grove cells. 
Upon the glass rod was attached a small piece of silvered glass, by 
means of which the light reflected from a paraffin lamp fell upon 
a scale divided to millimetres. The distance of the scale from the 
glass rod was about seven decimetres. The apparatus was arranged 
so that the glass rod was suspended within a glass jar or bottle, to 
get rid of currents of air. 
During the session 1872-73 thick flint glass tubes were 
employed for suspension, and an electro-magnet weighing about 
6 lbs. After that a rod of Faraday’s heavy glass was used, and an 
electro-magnet weighing about 50 lbs. 
