332 MR. P. W. BARLOW ON THE MOTION OF STEAM VESSELS. 



veniences in sea boats, and I therefore consider the wheels to have gained their 

 greatest limit in point of diameter. In the navigation of rivers, where a much 

 greater speed can be attained, wheels of larger diameter may probably be required. 



The ill effect of making the wheels of too large diameter, and the paddles too small, 

 is very sensibly exhibited in the experiments on the Medea ; her engines have the 

 same length of stroke as those of the Salamander, Phoenix, and Rhadamanthus ; and 

 the wheel is twenty-one feet in diameter to the centre of pressure, while those of the 

 latter vessels are not above eighteen feet five inches, or eighteen feet six inches. The 

 consequence is a considerable loss of power, from the greater velocity of the wheel 

 than of the ship. This loss of power is of course still small compared with that of 

 the common wheel when deeply immersed, so that in the experiment at Sheerness her 

 superiority of speed is perfectly consistent with the preceding calculations ; at the 

 same time I have no hesitation in saying, that an increase of speed of half a mile per 

 hour, at least, might be obtained by a smaller wheel and a greater surface of paddle- 

 board. 



This view of the case is satisfactorily confirmed by experiments on the Monarch 

 steam vessel. A former experiment on this vessel, not reported in the Table, with a 

 wheel of less diameter and larger floats, gave a speed above eleven miles per hour. 

 In the experiment given in the Table the average velocity is 10*8, so that a sensible 

 diminution of speed was produced by. enlarging the diameter of the wheel. 



