20 ANNUAL OF SCIENTIFIC DISCOVERY. 



need, he used for steering purposes. He thinks they are especially 

 applicable! to vessels of war, and has received the approval of 

 many naval officers and constructors. Pie has tested the wheels 

 on a model boat about 9 feet long, showing the advantage of 

 admitting air by a tube which can be opened and shut at will ; 

 the greater the velocity of revolution, the greater the advantage 

 of this admission in the saving of power. 



NEW ARRANGEMENT OF PROPELLER SCREWS. 



The improvement consists in quadrupling the number of screws, 

 that is, instead of working a boat with a single screw at the 

 stern, two screws are applied at either end of extra keels, which 

 are set on both sides of the bottom, and directly under the craft. 



It is claimed that a very great increase of speed is gained by 

 this new arrangement, and, in the trial trip at Troy, the propeller 

 certainly moved through the water with great celerity. 



Another unique arrangement consists of three vertical blades 

 placed equi-distant around an upright shaft at the stern of the ves- 

 sel, the lower end of the shaft working in a step on the prolonga- 

 tion of the keel. The shaft by which the blades are driven works 

 inside a hollow shaft, on which is secured a horizontal eccentric, 

 which connects by arms with the blades, and feathers them as 

 they rotate. No rudder is used with this propeller, the set of the 

 eccentric and blades, by means of a lever, determining the line 

 of the vessel's progress. 



The performances of the model are quite surprising. The ves- 

 sel was made to turn exactly on its centre repeatedly, without 

 going ahead, and a slight turn of the adjusting lever would send. 

 it either back or forward in a direct line, or in any circle desired, 

 ail without reversing the driving machinery and without the aid 

 of a rudder. 



HYDRAULIC PROPULSION. 



A feature in marine engineering, which has attracted much 

 attention, is Mr. Ruthven's system of hydraulic propulsion. 

 Among other advantages of this system, it gives a ship the power 

 of discharging a great quantity of water, and of thus keeping 

 afloat after she has sprung aleak or has been penetrated by shot. 

 It gives also facility of manoeuvring, while the propelling power 

 is far less liable to injury in action than either the screw or the 

 paddle. It has been successfully applied to the " Water witch," a 

 vessel of the British navy, and it is confidently expected that it 

 will prove of practical value. Though less exposed to shot than 

 the paddle-wheel, the bulky machinery of the turbine, above or 

 near the water-line, may be easily crippled. High speed has never 

 been attained by it, and its proved advantages are in the direction 

 of floating fire-engines, which have of necessity powerful pump- 

 ing gear for other purposes ; it also involves carrying a great 

 weight of water in the ship, increasing its displacement. As 

 applied to the " Waterwitch," it acts by the ejection of jets of 

 water from the sides of the vessel, a short distance above the 



