The author had occasion several years ago to design a double, pull-back drawbridge; and although he certainly evolved a structure that would work, he was far from satisfied with the design, so recommended another type of bridge for the crossing.

There is described in the Engineering Record of July 31, 1897, a double pull-back draw, which has just been completed over the River Dee at Queensferry, Scotland. It provides a clear opening of one hundred and twenty feet, and cost about $70,000.

Bascule bridges are those in which a shallow deck is raised from a horizontal position to a vertical or inclined one so as to let vessels pass. They may have either one or two leaves whose weight may be counterbalanced in various ways. When two leaves are used, they may be made to meet at mid-channel and form an arch, may rest on a central pier, may hang from a tower or from an overhead span, or may have hanging, hinged bents to rest on a submerged pier at the elevation of the bed of the channel.

For spans requiring leaves not longer than seventy-five feet the bascule type of bridge is very satisfactory; but beyond that limit the first cost of the structure begins to get too high as compared with another type of equally satisfactory structure, viz., the lift-bridge. Some bascule bridges, notably the Tower Bridge of London, England, have an overhead span to be used in connection with elevators by pedestrians when the lower deck is opened for the passage of vessels. The leaves of the Tower Bridge, which are each 113 feet long, do not raise quite to a vertical position, requiring one and a half minutes to open and as much more to close under favorable conditions of wind and weather, and sometimes twice as long when the conditions are unfavorable. The author has been told by an English gentleman resident in America, who made lately an investigation concerning the Tower Bridge, that the London people complain bitterly about the long time it takes to operate the structure. A lift-bridge similar to the Halsted Street Lift-bridge of Chicago, Ill., could have been  built instead,  which would raise  to full  height  in from thirty to