MECHANICS AND USEFUL ARTS. 13 



placed in a horizontal position, is a round iron case, in which there is 

 a wheel, having a shaft through a stuffing-box, on the upper or outer 

 side. The piston of the steam-engine is attached to the shaft-cranks, 

 and the steam-power is applied wholly to revolving the wheel in the 

 iron case, which, being made something like a fan-wheel, carries the 

 water with it in its revolutions. The water, in obedience to the laws 

 of centrifugal motion, presses towards the outer rim of the case with a 

 force proportionate to the speed, and escapes by an aperture and pipe 

 at each side, whence it is discharged by the nozzle into the sea. The 

 water is supplied to the iron case by a large, flat pipe, which has a 

 free communication with the sea by means of apertures in the bottom 

 of the vessel. The nozzle is above the water-line, and can be turned 

 by the seamen on deck with the greatest facility, so as to discharge 

 the water either towards the bow or stern. Discharging the water 

 astern makes the vessel go ahead ; when discharged towards the bow, 

 the vessel goes astern ; and when discharged downwards the vessel re- 

 mains stationary. These operations are effected without the engine be- 

 ing altered or stopped, a material improvement on the paddle-wheel ; 

 and as the elevation of one nozzle is rapidly altered, independently of 

 the other, ample facilities are given for turning the vessel. The ab- 

 sence of obstruction on the hull enables the vessel to use sails with as 

 much effect as a common sailing vessel, while the steam-power may 

 be perfectly combined with the action of the sails, an advantage de- 

 nied to a steam-vessel, except to a limited extent. Edinburgh Even- 

 ing Courant. 



IMPROVEMENT IN MARINE PROPULSION. 



MESSRS. JOHNSON, CAMMELL, & Co. have exhibited an improve- 

 ment in the machinery for propelling steam-vessels. The propellers 

 hitherto in use havft been invariably made from cast metal, and, when 

 at rest or in motion, are a perfect screw, always at the same pitch. 

 The improved flexible propeller to which we refer is made of steel, 

 well hammered and tempered, and set at an angle on the revolving 

 shaft. When at rest it. is a perfect plane, but when in action it 

 forms a screw, and, by the flexibility of the steel, assumes a finer or 

 a coarser pitch, according to the strength of the adverse action of the 

 water through which it moves. This circumstance imparts to the ves- 

 sel and machinery an easy action, especially in rough and heavy seas, 

 which has never been attained by the rigid screws now in use. Pro- 

 pellers manufactured according to this patent are not more than half 

 the weight of those made of cast metal, though the forgings are the 

 largest yet attempted to be made from steel. It has been ascertained 

 by experiment that, in point of speed, there is a gain of at least twenty 

 per cent. In heavy seas or rough weather this propeller can be easily 

 hoisted on board, by means of a simple block and tackle, thus saving 

 the expense of the machinery now used for raising the cast metal ones, 

 and, from being malleable and tough, it does away with the risk of 

 breakage, which necessarily ensues in the moving of a cumbersome 

 piece of cast metal. In cost there is a saving of about fifty per cent. 



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