MECHANICS AND USEFUL ARTS. 51 



SILVER'S MARINE GOVERNOR. 



The ordinary ball-governor was invented by James Watt as a part of the 

 steam-engine. In this instrument two heavy balls attached to the extremities 

 of two rods, articulated at their other end with a vertical shaft, arc made to 

 rotate with it, receiving motion from the engine. Centrifugal force is thus 

 produced, which overcomes gravity and forces the balls to separate and go 

 up in a circle to a distance proportional to the velocity of the machine. The 

 balls and rods are properly connected with a throttle-valve in the steam-pipe, 

 so that this is wide open when the velocity is small, and entirely closed the 

 moment a velocity is reached beyond which it is not desirable to go. This 

 instrument, depending on gravity for its accurate action, cannot be used on 

 board a ship, where the rolling and pitching would throw it in an inclined 

 position, in which the weight of the balls would make it act at the wrong 

 time. Mr. Thomas Silver, of Philadelphia, obviates this fault by adding two 

 more balls to equilibrate the two first, and by substituting the action of a 

 spring to that of gravity. The four balls of equal size are attached to two 

 rods working on a pin through the centre and through a small shaft. A 

 movable sleeve on this shaft is connected with the two rods half way between 

 the balls and the centre pin, and an adjustable steel spring pushes or pulls 

 constantly on the movable sleeve, in the proper direction to bring the four 

 balls close to the shaft. The movable sleeve is connected with the valve. 

 This instrument is of great service to paddle-wheel steamers, as in a heavy 

 sea it frequently happens that one wheel is entirely out of water, when the en- 

 gine acquires an undue velocity, technically called " racing," which, suddenly 

 checked by the reimmersiou of the wheel, may result in the breaking of the 

 shaft. But it is of a much greater import for propellers. In these ships the 

 screw is as often brought out of water by a heavy pitch, and as there is no 

 other wheel in the water to resist the power in a measure, the increase of 

 velocity is enormous. Two causes, then, combine for breaking the shaft 

 the first is, the sudden blow of the sea against the screw when reentering the 

 water; the other is, the side force exerted against the shaft when the plane 

 of rotation of a rapidly rotating body is suddenly changed. 



IMPROVEMENT IN PROPELLER ENGINES. 



The several direct-acting screw-propeller engines hitherto constructed are 

 objectionable in the following particulars, viz.: The horizontal engines 

 occupy too much space transversely in the vessel to admit of being placed in 

 the run. The vertical engines pass through the decks, and project so far 

 above the Avater-line as to be useless for war purposes ; and all approved 

 double engines operate on cranks placed at right angles to each other, which 

 involves as eries of bearings, much friction, and liability to derangement from 

 the shafts getting out of line. In addition to these imperfections, the extreme 

 shortness of the cranks, with the attendant great friction on the crank-pins 

 and journals, to say nothing of the heavy diagonal thrust of the connectini 1 ;- 

 rods, are serious defects in the direct-acting screw-propeller engines now in 

 common use. 



To obviate these difficulties, that well-known able, and veteran inventor, 

 John Ericsson, of hot air celebrity, has invented a useful improvement in 

 steam-engines for working propellers, which consists in the arrangement of 



