The following text may have been generated by Optical Character Recognition, with varying degrees of accuracy. Reader beware!

a MARINE REVIEW. New Forms of Bridges in Lake Harbor. On account of the growing commerce of the lakes and the crowded condition ot harbors and connecting channels, the ques- tion of constructing bridges that offer the least obstruction to navigation is receiving a great deal of attention. Since the pass- age, a short time ago, of the act giving to the secretary of war control of all navigable streams as regards the matter of bridges and other obstructions, railroad corporations and municipal au- thorities have been thwarted in efforts to erect bridges that were not acceptable to the war department, and as a result structures of various designs are proposed. The bridge shown in the ac- companying engraving is known as the Harman jack-knife, or folding bridge and is destined for the Chicago river at Canal street. 'The first bridge built under the Harman patent spans the Chicago river at Weed street, where the opening is 60 feet. The proposed Canal street bridge is to have a span of 80 feet, The detail of the bridge is as yet crude and clumsy, but it has been worked successfully. In the December number of the Engineiring Magazine, from which the engraving is taken, Mr. IT. Graham Gribble, civil en- gineer, describes the Harman bridge and discusses at some length the recent competition for a premium of $1,000 offered on plans t tnt : My i ---- BRIDGE OPEN Se ge ee en ee ae mee > "yw ETE OCIS Te re ee HARMAN LIFTING BRIDGE, CHICAGO RIVER. for a bridge at Duluth, Minn. 'The essential features of Har- man's folding bridge are that it is a double-jointed bascule," says Mr. Gribble," in which the outer joint permits the outer end of the bridge to fall down and so to cause the whole bridge to fold back against the pier. The portion of the bridge which rises forms an effectual barrier to the traffic while the bridge is open. It requires less counterbalancing than the ordinary bascule, is not liable to interfere with ships' rigging, and offers no resistance to wind, being folded up within the pier. It gives a clear water- way in the middle of the stream, and, last but not least, it is an economical bridge. Messrs. Shailer and Schniglau of Chicago ~-- are the contractors, and the detail has been worked out by the engineer of the company. Considerable ingenuity is shown in arrangement of motive power and counterbalancing. Instead of the unsightly rack-sectors usually seen in bascules, the bridge is operated by a solid-link chain and sprocket wheel under the floor. 'The counterbalance instead of being hung at the end of the shore arm, is, as will be seen, attached lower down. 'This was necessary on aceount of the composite movement of the bridge. Unlike those of ordinary bascules, the leaves, when reach- ing a certain point, tend to close of their own accord. A posi- tion of counterbalance was obtained from 'kinetic diagrams,which would as nearly as possible correspond in its effect to the com- bined effect of the rising and falling flaps. Both of the Chicago bridges are designed for ordinary street traffic. The designers red to adapt the bridge to railroad traffic and are confi- Sg af ontsining all the rigidity required. The fit of the ends is controlled by the outer forestay, but in addition a key will lock them together when closed. The tendency of the interme- diate joint to knuckle up under a passing load ts prevented by placing the center of the bridge and the two axles of rotation in one straight line. It can not be expected that a double-jointed bridge will be as rigid as one with a single joint, but it is still quite probable that the bridge may be adapted to railroad traffic and prove the best form for waterways of considerable width. At Duluth no decision has been made as to the kind of bridge to be constructed, although the competition resulted in twelve designs being submitted. 'The conditious called for a span 250 feet, single railway track, two electric railway tracks, two high- ways, and two sidewalks. The premium offered was $1,000 and was awarded to Messrs. Arentz and Sangdahl for a single sliding draw-bridge, estimated to cost $236,000. It was decided afterwards that the cost was too great, and it was proposed to construct a lifting bridge designed by J. A. Ll. Waddell of Kan- sas City. The towers were 170 feet high, and the estimated cost was $125,000. Pontoon bridges were submitted by BaiHs de la Rue and L. D. Grosvenor of Jackson, Mich.--one end pivoted the other on pontoon with propeller--estimate $108,000; similar construction by Onward Bates and J. N. Warrington of Chicago, estimate $80,000. Single swing bridges were submitted by T. A. McNicol of Providence, R.I., and double swings by HK. B. Jen- nings, of Springfield, Mass. A double-sliding draw-bridge was submitted by Sooysmith & Co. of New York and Chicago. May Result in the Building of War Vessels on the Lakes. In accordance. with a resolution passed at the last session of congress, the state department will shortly make a report rela- tive to conditions which have prevented the building of vessels of war on the lakes. It is understood that the report will show that notice of abrogation of the treaty of 1817, in so far as it ap* pertained to the number of vessels to be maintained by each country on the great lakes, was given under the act of 1866, but was immediately withdrawn because of complications then exist- ing between the two countries. The report will develop some very interesting facts and correspondence on the subject, and will also bring before congress official reports demonstrating the ability of lake ship builders to compete with builders on the coast in the construction of certain kinds of war vessels, and in fact the very largest of them if the water outlet to the seaboard would admit of their passage. Weakness in Deck on Account of Big Hatches. A naval architect of New York, who was recently shown some drawings of a steel freight steamer built on the lakes, writes a Cleveland friend as follows: "The data you send me is not sufficient from which to make satisfactory computations, but in looking over the drawings the weak point to me seemed un- doubtedly in the enormous hatches. 'Those caught my attention instantly, and I should expect that there, if anywhere, weakness would show itself. Nearly all of the deck is cut out, with little compensating material in deck or shear strakes in the wakes of the hatches."' Some builders are now strengthening new vessels in the parts to which the correspondent refers. Marine Engineering at the Fair. One of the divisions of the Engineering Congress, World's Columbian Exposition, will be devoted to marine and naval en- gineering and naval architecture. George W. Melville, engi- neer-in-chief of the United States navy, who is chairman of this division of the congress, says that preparations are not as yet entirely completed, but he anticipates a remarkably interesting series of meetings for the division, as there is assurance already of valuable papers from some of the most prominent marine en- gineers and naval architects both here at home and abroad. MARINE Revrew for one year and Patterson's Nautical Dictionary for $6.