38 ANNUAL OF SCIENTIFIC DISCOVERY. 



to a sixth of the consiimption of other marine engines. 4. The screw-pro- 

 peller possesses greater power of propulsion than any other propeller yet in- 

 troduced, by at least thirty per cent. 5. Attached to the engines is a power- 

 ful steam signal whistle, so constructed as to give out a code of signals, by 

 which captains of ships may communicate with each other, by sounds per- 

 fectly intelligible, at a distance of three or four miles apart. The object of 

 this portion of the invention is to prevent collisions at sea during dark nights 

 or foggy weather. The novelty in the steam-propeller is confined to the 

 manner of fixing the fans, so that each blade when revolving will clear the 

 other of back water. This adaptation seems extremely simple. The intro- 

 duction of a buoyant drum or boss, in which the root of the fan is fixed, 

 also reduces the weight of the shaft by about two-thirds. The trial vessel, 

 which will be readv for launching in a few davs, is of sixtvtons burthen, and 



, * ' V 



when fitted with her engines and stores will weigh only fourteen tons. She is 

 formed of plate iron one-eighth of an inch thick, witli angle irons an inch 

 and a half thick, and ribs fifteen inches apart. The inventor proposes to take 

 her to New York when finished. There can be no doubt that light iron 

 steamers, without cargo, and driven by high-pressure engines, can attain 

 very great speed in passing through the water, but it would be premature to 

 assert that the vessel now building will realize all the anticipations which 

 the builders have formed of her powers. 



Large Screw Steamer. The largest Screw Steamer hitherto constructed 

 has been launched at Glasgow during the past year. She is intended for 

 the Australian trade, and rates as of 1800 horse power. She is 2,800 tons bur- 

 then ; beam, forty-two feet ; length over all, 360 feet ; depth of hold, thirty-one 

 feet. She has t\vo direct action engines, six tubular boilers, and a three-bladed 

 propeller. She will carry 900 tons of goods, and her bunkers will stow 1,500 

 tons of coal enough for twenty-four days at full steam. It is unnecessary 

 to say that this vessel is of iron, as none but iron screw-propellers are made 

 in England. The number of these vessels is rapidly increasing in the mother 

 country, and they seem destined to supersede all others in the transportation 

 of goods of some value. 



CLIFFORD'S INVENTION FOR LOWERING BOATS. 



The following is a detailed description of Clifford's plan of lowering boats 

 at sea, which has been already alluded to in the Annual of Scientific Dis- 

 covery for 1857. The object of this important invention is to enable a man 

 placed in a suspended boat to lower it safely at a moment's notice, whether 

 it be empty or full of passengers, and whether the sea is smooth or rough, 

 whether the ship is at rest or in motion. In the centre of the boat, across 

 the keel, is a small windlass ; at both ends an ordinary pulley is fastened to 

 the keel, and immediately over each a friction pulley, (which will be 

 described hereafter) is suspended by ropes attached to the sides of the boat. 

 The boat being raised to the proper height by th'e usual means, and the ends 

 of two suspending ropes of exactly the same length being firmly secured to 

 the extremities of the davits, their other ends arc passed through the friction 

 pulleys, through the pulleys on the keel, and are loosely inserted in holes 



