This entire collection of pulleys and mechanism is established upon two brick foot bridges between which the bridge moves. These arched bridges offer no obstruction to navigation. Moreover, they always allow free passage to foot passengers, whatever be the position of the bridge. They are provided with four vertical apertures to the right of the suspension 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 since the year 1868, and has required but insignificant repairs. We think the adoption of it might be recommended for all cases in which a slight difference between the level of a railroad and that of a water course would not permit of the establishment of a revolving bridge.--_Le Genie Civil_. * * * * * ST. PETERSBURG A SEAPORT.