[Illustration:  Fig. 252.  Kellogg Drop and Jack]

Kellogg Type:—­A very widely used scheme of mechanical restoration is that employed in the Miller drop and jack manufactured by the Kellogg Switchboard and Supply Company, the principles of which may be understood in connection with Fig. 252.  In this figure views of one of these combined drops and jacks in three different positions are shown.  The jack is composed of the framework B and the hollow screw A, the latter forming the sleeve or thimble of the jack and being externally screw-threaded so as to engage and bind in place the front end of the framework B.  The jack is mounted on the lower part of the brass mounting strip C but insulated therefrom.  The tip spring of the jack is bent down as usual to engage the tip of the plug, as better shown in the lower cut of Fig. 252, and then continues in an extension D, which passes through a hole in the mounting plate C.  This tip spring in its normal position rests against another spring as shown, which latter spring forms one terminal of the drop winding.

The drop or annunciator is of tubular form, and the shutter is so arranged on the front of the mounting strip C as to fall directly above the extension D of the tip spring.  As a result, when the plug is inserted into the jack, the upward motion of the tip spring forces the drop into its restored position, as indicated in the lower cut of the figure.  These drops and jacks are usually mounted in banks of five, as shown in Fig. 253.

[Illustration:  Fig. 253.  Strip of Kellogg Drops and Jacks]

Western Electric Type:—­The combined drop and jack of the Western Electric Company recently put on the market to meet the demands of the independent trade, differs from others principally in that it employs a spherical drop or target instead of the ordinary flat shutter.  This piece of apparatus is shown in its three possible positions in Fig. 254.  The shutter or target normally displays a black surface through a hole in the mounting plate.  The sphere forming the target is out of balance, and when the latch is withdrawn from it by the action of the electromagnet it falls into the position shown in the middle cut of Fig. 254, thus displaying a red instead of a black surface to the view of the operator.  When the operator plugs in, the plug engages the lower part of an =S=-shaped lever which acts on the pivoted sphere to restore it to its normal position.  A perspective view of one of these combined line signals and jacks is shown in Fig. 255.

A feature that is made much of in recently designed drops and jacks for magneto service is that which provides for the ready removal of the drop coil, from the rest of the structure, for repair.  The drop and jack of the Western Electric Company, just described, embodies this feature, a single screw being so arranged that its removal will permit the withdrawal of the coil without disturbing any of the other parts or connections.  The coil windings terminate in two projections on the front head of the spool, and these register with spring clips on the inside of the shell so that the proper connections for the coil are automatically made by the mere insertion of the coil into the shell.