326 Prof. Callan on the Induction Apparatus. 
current is produced in each of them as well as in all contiguous 
conductors. Both, I think, may be satisfactorily proved. First, 
every one knows that the iron core is magnetized by the primary 
current. Secondly, the primary coil itself is a magnet as long 
as it is connected with the battery; for every wire or conductor 
through which a voltaic current flows has magnetic properties : 
one of its sides will attract the north pole of a magnetic needle, 
and the opposite will attract the south pole; so that if the wire 
be placed over the needle at rest, the latter will be deflected from 
the magnetic meridian. The wire, or conductor of a galvanic 
current has its magnetic poles, not at its extremities, but at its 
opposite sides; so that were the wire divided into two halves 
along its length, one half would be a north and the other a south 
magnetic pole. The magnetic axis of such a wire is one of its 
diameters, or a line joining its opposite sides. Thirdly, the 
secondary coil is a magnet when the primary coil is connected 
with the battery. This is evident when the secondary coil is 
made of iron wire; for the primary current magnetizes iron by 
which it is surrounded as well as iron enclosed within it: it in- 
duces in each section of the surrounding as well as of the enclosed 
iron, an electrical current which magnetizes the iron. I have 
found by experiment that iron outside the primary coil is not so 
strongly magnetized as iron enclosed within it. When, as is 
commonly the case, the secondary coil is made of copper wire, it 
is also a magnet; for the primary current induces an electrical 
current in each spiral of the secondary coil of copper, as well as 
in each section of the iron core. This current magnetizes each 
spiral of the copper coil, and makes the whole coil a magnet at 
the moment the primary coil is connected with the battery. 
Now we must supposé, that as the primary current, whilst it 
continues to flow, maintains in the iron core the magnetic power 
produced by the currents induced in each section of the iron at 
the moment the primary coil is connected with the battery, 
although these currents last but an instant, so also the same 
primary current will maintain in each of the spirals of the copper 
coil the magnetism giyen to them by the currents induced in 
them at the moment the battery connexion is made. There is 
no reason why the continuance of the primary current should 
not maintain its first effect in the copper spirals as well as in 
the iron, since the first effect is the same in both, viz. the mag- 
netization of both. Hence, when the primary wire of an induc- 
tion coil is connected with a battery, the secondary coil is always 
a magnet, as well as the core and primary coil; and therefore in 
every induction coil we have three magnets so long as its pri- 
mary coil is connected with a voltaic battery ; and the three lose 
their magnetism the moment the battery communication is 
