ON NEW MAGNETIC ACTIONS. 
23 
and attached, at the upper end, to the sliding rod, and at the lower end to a stirrup 
of paper, in which anything to be experimented on could be sustained. 
2249. Another very useful mode of suspension was to attach one end of a fine 
thread, six feet long, to an adjustable arm near the ceiling of the room, and termina- 
ting at the lower end by a little ring of copper wire ; any substance to be suspended 
could be held in a simple cradle of fine copper wire having eight or ten inches of 
the wire prolonged upward; this, being bent into a hook at the superior extremity, 
gave the means of attachment to the ring. The height of the suspended substance 
could be varied at pleasure, by bending any part of the wire at the instant into the 
hook form. A glass cylinder placed between the magnetic poles was quite sufficient 
to keep the suspended substance free from any motion, due to the agitation of the 
air. 
2250. It is necessary, before entering upon an experimental investigation with such 
an apparatus, to be aware of the effect of any magnetism which the bodies used may 
possess; the power of the apparatus to make manifest such magnetism is so great, 
that it is difficult on that account to find writing-paper fit for the stirrup above men- 
tioned. Before therefore any experiments are instituted, it must be ascertained that 
the suspending apparatus employed does not point, i. e. does not take up a position 
parallel to the line joining the magnetic poles, by virtue of the magnetic force. 
When copper suspensions are employed, a peculiar effect is produced (2309.), but 
when understood, as it will be hereafter, it does not interfere with the results of ex- 
periment. The wire should be fine, not magnetic as iron, and the form of the sus- 
pending cradle should not be elongated horizontally, but be round or square as to 
its general dimensions, in that direction. 
2251. The substances to be experimented with should be carefully examined, and 
rejected if not found free from magnetism. Their state is easily ascertained ; for, if 
magnetic, they will either be attracted to the one or the other pole of the great 
magnet, or else point between them. No examination by smaller magnets, or by a 
magnetic needle, is sufficient for this purpose. 
2252. I shall have such frequent occasion to refer to 
two chief directions of position across the magnetic field, ? 
that to avoid periphrasis, I will here ask leave to use a 
term or two, conditionally. One of these directions is 
that from pole to pole, or along the line of magnetic force ; 
I will call it the axial direction : the other is the direction 
perpendicular to this, and across the line of magnetic force ; and for the time, and as 
respects the space between the poles, I will call it the equatorial direction. Other 
terms that I may use, I hope will explain themselves. 
