illustrated in Fig. 55.

It cannot be denied that one of the principal items of maintenance of
subscribers' station equipment has been due to the breakage of
receiver shells. The users frequently allow their receiver to fall and
strike heavily against the wall or floor, thus not only subjecting the
cords to great strain, but sometimes cracking or entirely breaking the
receiver shell. The innovation thus proposed by the Dean Company of
making the entire receiver shell of steel is of great interest. The
shell, as will be seen, is entirely insulated from the circuit of the
receiver so that no contact exists by which a user could receive a
shock. The shell is enameled inside and out with a heavy black
insulating enamel baked on, and said to be of great durability. How
this enamel will wear remains to be seen. The insulation of the
interior portions of the receiver is further guarded by providing a
lining of fiber within the shell at all points where it seems possible
that a cross could occur between some of the working parts and the
metal of the shell. This type of receiver has not been on the market
long enough to draw definite conclusions, based on experience in use,
as to what its permanent performance will be.

Thus far in this chapter only those receivers which are commonly
called _hand receivers_ have been discussed. These are the receivers
that are ordinarily employed by the general public.

[Illustration: Fig. 57. Operator's Receiver]

Operator's Receiver. At the central office in telephone exchanges
the operators are provided with receivers in order that they may
communicate with the subscribers or with other operators. In order