22 ANNUAL OF SCIENTIFIC DISCOVERY. 



Paddle -Wheel Engines. The engines for the paddle-wheels, which were 

 designed and built by Mr. Scott llussell, are oscillating engines, of the fol- 

 lowing dimensions : 



Nominal horse power, 1000 



Number of cylinders, 4 



Diameter of each cylinder, 74 in. 



Length of stroke, 14 ft. 



Strokes per minute, 14 



The weight of one of the cylinders, including piston and piston-rod, is 

 thirty-eight tons. Each pair of cylinders, with its crank, condenser, and 

 air-pump, forms in itself a complete and separate engine, and each of the 

 four cylinders is constructed so as to permit instant disconnection, if re- 

 quired, from the other three; so that the whole form a combination of four 

 engines, complete in themselves, whether worked together or separately. 

 The two cranks are connected by a friction-clutch, so that the two pairs of 

 engines can be connected or disconnected at a moment's warning, and by a 

 single movement of the hand. The engines are provided with expansion- 

 valves, throttle-valves and governors, all constructed on the most improved 

 principles, and arranged for working in the most efficient manner. The 

 combined paddle-engines will work up to an indicator-power of three thou- 

 sand horses of thirty-three thousand pounds when working eleven strokes 

 per minute, with steam in the boiler at fifteen pounds upon the inch, and 

 the expansion-valve cutting off at one-third of the stroke. But all the parts 

 of the engines are so constructed and proportioned, that they will work 

 safely and smoothly at eight strokes per minute, with the steam at twenty- 

 five pounds, and full on without expansion (beyond what is unavoidably 

 effected by the slides), or at sixteen strokes per minute, with the steam in 

 the boiler at twenty-five pounds, and the expansion-valve cutting off at 

 one-fourth of the stroke. Under these last-named circumstances, the pad- 

 dle-engines alone will give a power of about five thousand horses. 



Paddle-Engine Boilers. There are four boilers for the paddle-engine, 

 seventeen feet nine inches long, seventeen feet six inches wide, and thirteen 

 feet nine inches high, each weighing about fifty tons, and containing forty 

 tons of water. They are tubular boilers, manufactured of wrought plate- 

 iron, with brass tubes of three inches diameter. There are ten furnaces in 

 each boiler, five on either side, and two boilers in each boiler room. Each 

 boiler room is supplied with air by four ventilators or shafts, seven feet 

 long by five feet Avide, which go up to the upper deck, where they arc grated 

 over, and up two of them there are gangways, one to each stoke-hole. 

 These paddle-boilers are in two distinct sets, and each set is equal to supply, 

 with steady, moderate firing, steam for an indicator of one thousand eight 

 hundred horse power; though, with full firing, each set of two gives steam to 

 the amount of two thousand five hundred horse power, or five thousand 

 horse power in all. 



The Screw-Propeller. The screw-propeller, which is twenty-four feet in 

 diameter, and forty-four feet pitch, is by far the largest ever made. I;s 

 four fans, which were cast separately, and afterwards fitted into a large cast- 

 iron boss, have been compared to the blade-bones of some huge animal of 

 the prc-Adamite world. The weight of the screw is thirty-six tons. The 

 propeller-shaft, destined to move the screw itself, is one hundred and sixty 

 feet in length, and weighs sixty tons. The after-length of this shaft, forty- 



