40 ANNUAL OF SCIENTIFIC DISCOVERY. 



top and sides, capable of sustaining great pressure the usual appendages, 

 knees, angle-iron plates, and rivets, for gunwale fastenings, are entirely dis- 

 pensed with. 



Straining of Ships in Launching and Docking. The late George Steers, 

 who was considered the most eminent ship-builder of our own or any other 

 times, contended that it is a common evil to strain and " hog" large ships, by 

 supporting them too exclusively by their keels in docking. The case is nearly 

 as bad in launching, the bilgeways being so near the keel on each side that 

 the whole weight of the vessel is supported on a narrow line. He argued 

 that much of the distortion observed in vessels a short tune hi service is due 

 to the straining received in this manner before their completion. The steam- 

 frigate Niagara was built without much regard to the old rules of the naval 

 constructors, and is lighter timbered but heavier fastened than ordinary war 

 vessels of her size ; and to avoid the evil alluded to, she was strongly truss- 

 ed on the inside to support the bilge before launching. The same bracing, 

 which consisted of strong chains from the bilge passing over a tall, stiff 

 framework erected upon the keelsons, remained in the ship during her dock- 

 ing, and the result was that the hull is not bent more than one inch hi any 

 direction from her form as moulded. 



Hirundine Propeller. This propeller, for which great results are claimed 

 hi England, is thus constructed : A flat, many-jointed or elastic band, repre- 

 senting the leech, is extended edgewise to the horizon in a curved undulated 

 line, within a square-sided chamber or tube, formed through the whole length 

 of the vessel below the water line, and open at both ends. The vessel is 

 built without distinction of stem or stern to move in either direction. The 

 undulatory action is produced by rods passing at regular distances from the 

 band to cranks or eccentrics, set hi a spiral series on a shaft, which runs 

 parallel to the tube, and this at each revolution raises and depresses the band 

 in a continuous wave-like movement throughout its entire length. By this 

 process, the whole column of water in the tube is discharged with great impe- 

 tus from one of the ends, and the ship is impelled onwards in the opposite 

 direction. 



Robinson's Screw and Side-Lever Steering Gear. In this arrangement the 

 steering wheel is set a little out of the keel line of the ship, on the port side ; 

 and its spindle, which is carried in two-end pedestal bearings, is cut with a 

 stout square screw thread. This screw spindle has upon it a long traversing 

 nut, fitted with a pah 1 of diametrically opposed joint stud pins, for connexion 

 with the end of the sliding lever, which forms the actual tiller. The joint end 

 of this lever is made with a fork and straps, for embracing the stud-pins of the 

 nut. The remaining portion of the lever is a plain cylinder, and it is entered 

 freely through a long inclined eye-piece on the rudder-head, which is, of 

 course, on the starboard side of the screw spindle, and opposite to the longi 

 tudinal centre of the latter. The eye on the rudder-head works on a stud 

 pin, so that, in all circumstances, the action is easy and free from strain. 

 As the screw spindle nut traverses forward or aft, in obedience to the turn of 

 the steering wheel, it carries with it the outer end of the tiller, which thus 

 acts as a lever to turn the rudder ; and as the nut must always move in a 



