chains, in order to allow of the passage of the latter. The girders that
support the pulleys rest at one extremity upon the upper part of the
bridges, and at the other upon solid brick pillars with stone caps.

Finally, in order to render the descent of the bridge easier, there are
added to it two water tanks that are filled from the station reservoir
when the bridge is in its upper position, and that empty themselves
automatically as soon as it reaches the level of the railroad tracks.

A very simple system of fastening has been devised for keeping the
bridge in a stationary position when raised. When it reaches the end of
its upward travel, four bolts engage with an aperture in the suspension
rod and prevent it from descending. These bolts are set in motion by
two connecting rods carried by a longitudinal shaft and maneuvered by a
lever at the end of the windlass.

At the lower part the bridge rests upon iron plates set into sills. It
is guided in its descent longitudinally by iron plates that have an
inclination which is reproduced at the extremities of the bridge
girders, and transversely by two inclined angle irons into which fit the
external edges of the bottoms of the extreme girders.

[Illustration: FIG. 2.--ELEVATION AND PLAN.]

The total weight of the bridge is, as we have said, 44,000 pounds, which
is much less than would have been that of a revolving bridge of the same
span. The maneuvering of the bridge is performed with the greatest ease
and requires about two minutes.

This system has been in operation at the market station of La Vilette