THE UNITED STATES OF AMERICA. 109 



that the force of the engines employed exceeded that which had been used in some American 

 vessels which had far less speed. Neither was the relation of the power of the engine, estimated 

 in the usual manner, to the tonnage of the vessel, greater than that found in European 

 steamers, whose velocity does not appear, at that time, to have exceeded ten miles per hour. 

 Besides, it cannot be denied that the advantage in the finish and workmanship of the engines 

 was on the side of the European vessels. We may therefore inquire to what circumstances it 

 was owing, that a rate of speed, which a high British authority has very recently declared to be 

 incredible, should be actually obtained. We ascribe this chiefly to the great difference in the 

 principles which governed the structure of the engines in the two different countries. In the 

 modifications of the original form of the engine of Fulton, the English engineers, whose efforts 

 were principally directed to the navigation of stormy seas, thought it indispensable that the 

 machinery should be included beneath the deck of the vessel. The stroke of the piston and 

 the length of the crank were therefore diminished below the proportion originally chosen by 

 Watt. In America, the vessels being principally intended for the navigation of rivers, no 

 such change occurred; and when it became necessary to make the 'New Philadelphia' compete 

 with vessels driven by more powerful engines, Stevens increased the length of the stroke and of 

 the crank. The new relation between the diameter and length of the cylinder thus obtained, 

 was followed, or even exceeded, in all subsequent engines. No change was made in the 

 dimensions of the boiler, but the additional force was obtained by causing the steam to act 

 expansively. The latter method was attended by an anomaly, which is however readily 

 explained, when it is considered that the relative velocity of the circumference of the wheel is 

 constant. It was not found that the steam, although cut off, at first at half stroke, was much 

 increased in tension. The most obvious effect of the method was an increase in the velocity 

 of the piston, by which the steam was prevented from accumulating. 



When we consider the wheel as a body revolving on an axis, and which meets with a 

 resistance, whose resultant is applied to a point at no great distance from its circumference, 

 it will be obvious that there will be a point, to which, if the crank be applied, the whole force 

 of the engine will be exerted to overcome the resistance ; but if the crank be applied to any 

 other point, a part of the force will be wasted upon the axle itself. Now, even in the long 

 stroke usual in the modern American engines, it does not appear that the crank extends as 

 far as this most favourable point ; but in the short stroke of the English engines a large 

 proportion of the whole power is lost. 1 This advantage is, however, at present less sensible 

 in the American steam boats ; for the principle of using cylinders of great length having been 

 introduced, the next step was to increase the diameters of the wheels. The object intended 

 to be gained by the latter change was an increase in the velocity of the circumference of the 

 wheel, for the constructors of steam boats seem to have reached the conclusion that every 

 addition to this velocity would add as much to that of the vessel. In one instance the 

 diameter of the water wheels has been increased to thirty feet, and the stroke of the piston to 

 twelve feet. 



As an additional means of obtaining high velocities in the piston, the dimensions of the 

 valves and steam pipes of the American engines have been increased beyond the proportion 

 used by Watt. The flow of the steam from the boiler is thus rendered more rapid, and the 



1 The author must here allude to the friction caused by the pressure on the shaft : no loss of power can otherwise result 

 from the mechanical arrangement. ED. 



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