LOCOMOTION BY RIVER AND RAILWAY. 



boats have cylinders seventy-six inches in diameter, and fifteen 

 feet stroke. The steam has forty pounds pressure in the boiler, 

 and is cut off at half-stroke. The wheels, which are forty-five 

 feet in diameter, make sixteen revolutions per minute. The speed 

 of the circumference of the wheel will therefore be twenty-five 

 miles an hour ; so that, if the speed of the boat be twenty miles an 

 hour, we have the difference, five miles, giving the relative move- 

 ment of the edge of the paddle-boards through the water. 



To ascertain the power developed by these engines, let us suppose 

 the mean effective pressure on the piston, taking into account the 

 degree of vacuum produced by the condenser, and supposing the 

 steam to be cut off at half-stroke, to be 40 Ibs. per square inch, the 

 area of the piston 4536 square inches, and the stroke 15 feet; the 

 piston moves through 30 feet during each revolution of the wheels ; 

 and since 16 revolutions take place per minute, we shall find the 

 effective force developed by the piston by multiplying its area, 

 4536, by twice the length of the stroke, which is 30, and by 16, 

 which is the number of revolutions per minute. This product 

 multiplied by 40, the number of pounds effective pressure per 

 square inch, gives 87,091200 Ibs. raised one foot high per minute 

 as the power developed by the engine. This is equivalent, 

 according to the ordinary mode of expressing steam power, to 

 2,640 horse power. 



Whatever allowance, therefore, may be made for friction, &c., 

 it is clear that the effective power thus obtained must be greater 

 than anything hitherto executed on water. 



The increase of the dimensions of these vessels and their 

 machinery has been attended with a greatly augmented economy 

 of fuel. 



On comparing the Hendrik Hudson, for example, with the Troy, 

 a vessel formerly well known, plying between New York and 

 Albany, it has been found that when the speed of the former is 

 reduced to an equality with that of the latter, the trip between 

 New York and Albany being performed in the same time, the 

 former consumed thirteen tons of coal while the latter consumed 

 twenty ; yet the displacement of the Hendrik Hudson, owing to 

 its increased dimensions, is nearly twice that of the Troy. 



The ease with which these vessels of extraordinary length and 

 beam and small draft move through the water is very remarkable. 

 The results of their performance show that the resistance per 

 square foot of immersed midship section is not perceptibly in- 

 creased by the increased length of the vessel, and the consequently 

 augmented surface and friction. This anomaly has not been 

 explained, but it is certain that the increased length does not 

 diminish the effect of the moving power in any perceptible degree. 

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