HUDSON STEAMEKS. 



increased consumption of fuel per hour would be necessary in the 

 proportion of 3 to 5 ; but the waste incurred by urging the 

 blowers so as to produce a sufficiently vivid combustion is so 

 irivat, that it is practically found that the consumption of fuel is 

 increased in a much higher ratio than that which results from the 

 increased resistance, and indeed in some cases that the increase .of 

 three or four miles an hour on eighteen miles will cause nearly 

 triple the consumption of fuel. 



12. Much of the efficiency of these engines arises from the 

 application of the expansive principle ; but to this there has been 

 hitherto a limit, owing to the inequality of the action of the piston 

 when urged by expanding steam on the crank. When the steam 

 is cut off at less than half-stroke, the force of the piston is 

 diminished before the termination of the stroke to less than one 

 half its original amount. This inequality is aggravated by the 

 relative position of the crank and connecting rod, the leverage 

 diminishing in nearly the same proportion as the power of the piston 

 diminishes. On this account it has not been found generally 

 practicable to cut off the steam at less than half-stroke. 



13. It must be observed, in relation to the navigation of these 

 eastern rivers, that the occurrence of explosions is almost unheard- 

 of. During the last ten years, not a single catastrophe of that 

 kind has occurred on them, although cylindrical boilers ten feet 

 in diameter, and composed of plating -j^ths of an inch thick, 

 are commonly used with steam of fifty pounds pressure above 

 the atmosphere. 



14. It will be seen by the table given above, that the paddle- 

 wheels used on these rivers have extraordinary magnitude. 

 There is nothing particular in their construction. The split 

 paddle-board, which was adopted about ten years since, has been 

 discontinued, and has given way to the simple and continuous 

 paddle-board. These boards, however, are generally placed alter- 

 nately at greater and less distances from the centre, somewhat like 

 a break-joint. Wooden spokes, with cast-iron centre pieces, are 

 generally adopted. 



The steam is universally worked with expansion, the valves for 

 its admission and emission being moved independently of each 

 other. A separate engine is generally provided for driving the 

 blowers, and a cylindrical fan-blower is employed for each boiler. 

 Some of these blowers are ten feet in diameter, being driven by a 

 crank placed on their axle, which receives its motion from the 

 small independent engine. 



lo. The great power developed by these river engines is due, 

 not so much to the magnitude of their cylinders, as the pressure 

 of steam used in them. Some of the most recently constructed 



25 



