rection (from the right in the
engraving) touches it, it will be seen that it must not only depress it,
but produce a slight forward motion, causing a corresponding rotary
motion in the rock shaft which actuates the apparatus. On the other
hand, when a train is approaching from the other direction, or has
already passed the crossing, its wheels strike first the curved plate to
the left of the illustration, and by means of the peculiar link
connections shown, depress the rock plate so as to clear the wheels
before the wheels touch it, but the depression is directly vertical, so
that it does not give any horizontal motion to it, which would have the
effect of actuating the rock shaft. Consequently, trains pass over the
apparatus in one direction without having any effect upon it whatever,
the different point at which the same force is applied to the rock plate
giving the latter an entirely different motion.

[Illustration: FIG. 2.--MAGNETO-ELECTRIC CROSSING SIGNAL]

The slight rotary motion which is in this way communicated to the rock
shaft, when a train is approaching in the right direction, compresses a
spring inside the case. As each wheel passes off the rock plate, the
reaction of the spring throws it up again to its former position, giving
additional speed to the gearing within, which is set in motion at the
passage of the first wheel, and operates the electric "generator." The
spring is really the motive power of the alarm. A small but heavy
fly-wheel is connected with the apparatus, the top of which is just
visible in the engraving, which serves to store up power to run the
"generator," which is nothing more than a small dynamo, for the
necessary number of seconds after the rear of the train has passed. The
dynamo dispenses with all need for batteries, and reduces the work of
maintenance to occasionally refilling the oil-cups and noticing if any
part has been broken.

A suitable wire circuit is provided, commencing at the generator with
insulated and protected wire, and continued with ordinary telegraph
wire, which can be strung on telegraph poles or trees leading to the
electric gong, Fig. 2, which rings as long as the armature revolves. It
is a simple matter so to proportion the mechanism for the required
distance and speed that the revolutions of the armature and the ringing
of the gong shall continue until the train reaches the crossing; and as
each wheel acts upon the apparatus, the more wheels there are in