168 New Magnetic Electrical Machine. 
is made from a bar of two and one half inch iron, and fourteen 
feet long. Its lifting power is about one thousand five hundred 
pounds, and when the battery and armature are removed, it retains 
a permanent lifting power of fifty pounds. Struck with this cu- 
rious fact, I was led to the construction of the compound electro- 
magnet. My first experiment was made with three separate lay- 
ers of coiled wire round a wooden spool ten inches long, witha 
bar of soft iron enclosed. 'This was connected with two pairs of 
plates and the spark and shock observed. ‘The bar of iron was 
then removed, and a bundle of annealed large iron wire, intro- 
duced in its place. The sparks and shocks were increased to a 
surprising degree. I then took a bundle of smaller wires four 
inches long and wound them with only two layers of continuous 
wire. The spark from this was as intense as that given by the 
large bar in the spool. I next took seven pieces of good hoop 
iron, well annealed, one inch wide, one fourteenth of an inch thick 
and eight inches long. These were firmly rivetted together, and 
the angles of the compound bar thus made, were rounded to pre- 
vent cutting the wire. Four layers of coiled wire were then 
wound upon it, and their ends attached to two connecting wires. 
can be imagined more intense and beautiful than the 
sparks produced by this little compound magnet. When a piece 
of iron is burned with it, the ignited particles are frequently frowns 
off, the distance of two feet, and occasionally fall to the floor. 
For its size, it is the strongest electro-magnet I have ever known, 
and when the battery is withdrawn, there is not magnetism 
enough retained, to affect a very delicate needle. From this per- 
fect neutralization of power, arises in great measure, the intensity 
of the secondary current. The neutrality is partly due to the re- 
duced size of the bars, but chiefly to the action of their similar 
poles upon each other, when the exciting cause is withdrawn. 
Fig. 3, represents a small elec- 
tro-magnetic bar, mounted for 
rotation, with my pole changer 
attached, which is shown at a. 
6 b, are the conducting tangent 
Springs ; ¢ ¢, mercury cups for 
connexion with the battery. No 
stationary magnets are here used, 
the instrument being made with 7 
