at is wound with enamel
wire, by sheets of paper or thin oiled cloth.

[Illustration: Fig. 99. Electromagnet with Bare Wire]

In Fig. 99 is shown a method, that has been used with some success, of
winding magnets with bare wire. In this the various adjacent turns are
separated from each other by a fine thread of silk or cotton wound on
beside the wire. Each layer of wire and thread as it is placed on the
core is completely insulated from the subsequent layer by a layer of
paper. This is essentially a machine-wound coil, and machines for
winding it have been so perfected that several coils are wound
simultaneously, the paper being fed in automatically at the end of
each layer.

Another method of winding the bare wire omits the silk thread and
depends on the permanent positioning of the wire as it is placed on
the coil, due to the slight sinking into the layer of paper on which
it is wound. In this case the feed of the wire at each turn of the
spool is slightly greater than the diameter of the wire, so that a
small distance will be left between each pair of adjacent turns.

Upon the completion of the winding of a coil, regardless of what
method is used, it is customary to place a layer of bookbinders' cloth
over the coil so as to afford a certain mechanical protection for the
insulated wire.

_Winding Terminals_. The matter of bringing out the terminal ends of
the winding is one that has received a great deal of attention in the
construction of electromagnets and coils for various purposes. Where
the winding is of fine wire, it is always well to reinforce its ends
by a short piece of larger wire. Where this is done the larger wire is
given several turns around the body of the coil, so that the finer
wire with which it connects may be relieved of all strain which may be
exerted upon it from the protruding ends of the wire. Great care is
necessary in the bringing out of the inner terminal--_i.e._, the
terminal which connects with the inner layer--that the terminal wire
shall not come in contact with any of the subsequent layers that are
wound on.

[Illustration Fig. 100. Electromagnet with Terminals]

Where economy of space is necessary, a convenient method of
terminating the winding of the coil consists in fastening rigid
terminals to the spool head. This, in the case of a fiber spool head,
may be done by driving heavy metal terminals into the fiber. The
connections of the two wires leading from the winding are th