The Royal Society Socree, 431 
- An ordinary steam-engine of 15-horse power, was placed. 
outside the building, and a driving strap brought through 
the window of the room. Here, on the floor, guarded all 
round by plates of metal, stood a huge induction magnet 
surmounted by a battery of smaller natural magnets; wheels 
and driving bands connected its various parts with the 
steam-motive power. The main parts of the machine are 
two. First, a magneto-electric portion; and, second, an 
electro-magnetic one—the former being only considered an 
accessory. Taking this part first, it consists of 20 perma- 
nent horse-shoe magnets fixed to a magnet cylinder; each 
of the permanent magnets being about 17 inches high and 
14 inches broad, and capable of sustaining a weight of 
about 30lbs. The magnet cylinder is formed of two seg- 
mental pieces of cast-iron, separated by two pieces of brass, 
the whole being bolted together in such a way as to consti-_ 
tute a compound hollow cylinder of brass and iron, the 
brass not being a conductor of magnetism, isolating each 
half from the other. The bore of the cylinder is 34 inches 
in diameter. Intothis is inserted an armature, of the form 
used by Mr. Siemens, and made of cast iron wound longi- 
tudinarily with about 80 feet of covered copper wire, the 
inner end of which is placed in good metallic contact with 
the armature, and its outer extremity connected with the. 
insulated half of the commutator. This armature is made 
to revolve inside the magnetic cylinder at about 2,000 re- 
volutions per minute, and consequently, as in each revolu- 
tion it is magnetised in two directions, 4,000 waves of elec- 
tricity are transmitted from it in that time. The mag- 
netism so generated, is carried to the polar terminals of. 
the great electro-magnet, consisting of two plates of rolled 
iron 48 inches in length, 39 inches wide, and 14 inches in 
thickness. Bolted to the upper and lower extremities of 
the plates are iron bars 6 inches wide and 2 inches thick. 
The extremities of the plates are united by a hollow bridge, 
made of rolled iron, 43 inches long, and 16 inches wide. 
Each side or limb of this electro-magnet is coiled with an 
insulated conductor consisting of 13 strands of copper wire, 
125 inches in diameter, bound together with a double 
covering of linen tape. In length this rope is 4,800 feet, 
and the total weight of the two coils is over 1} tons. The 
magnet cylinder for this machine consists of two masses of 
cast iron 50 inches in length, separated from each other by 
blocks of brass. An armature, similar in plan to that used 
in the magneto-electric machine, but enormously larger in 
NEW SERIES.—VOL. I. NN 
