SECT, x.j OF STEAM NAVIGATION. 309 



has been greatly overrated, and most of the contrivances are directed to remove it 

 either wholly or in part. The methods proposed are of two kinds. In one a 

 gradual change of position of the paddle is produced by the movement of the 

 wheel ; completely forgetting, that by loss of the velocity, the decrease of force is as 

 the square, while by variation of direction the loss is only in simple proportion. 

 Mr. Oldham, of the Bank of Ireland, proposed a plan for these revolving paddles, 

 to avoid the defects of the fixed paddles commonly used ; and states, that the violent 

 action of the paddles of common wheels, in striking the water in a rough sea, is 

 entirely removed by the use of the revolving paddles, as they enter and rise out of 

 the water with a peculiarly soft and easy motion. We can only regret that so 

 much ease cannot be obtained without a considerable and constant sacrifice of 

 power. 



The other method is to cause the paddles to change at once to a new position at 

 two points in the revolution, by means of proper catches and mechanism. This is 

 a better method for cases where the wheels are to work when deeply immersed in 

 water ; but such wheels require to be made so very strong and powerful, that there 

 appears to be small probability of the machinery keeping in order. 



The plan of making paddles which seems most plausible, is to have a pair of 

 wheels at each side of the vessel, having two endless chains acting on them, with 

 paddles fixed on these chains. As the chain passes in one direction, the paddle 

 boards are immersed in the water, and return in the opposite direction out of the 

 water ; the two wheels around which they pass being partially under water. The 

 whole of the impulse given by these boards from the lower part of one wheel to the 

 lower part of the other, seems as though it would be direct and effectual ; and it is 

 stated, that so far as the plan has been tried on a very small scale, it has been 

 successful. It is said however by Buchanan to have been tried on the Duke of 

 Bridgwater's canal, where it did not give satisfaction ; and the reason not being 

 assigned, we must endeavour to show whether or not the arrangement can have 

 greater effect than the common paddle wheel. 



If a wheel have a sufficient number of paddles to force the whole of the fluid 

 opposed to the area of the paddle into motion, it is obvious that any continuation of 

 "the line of action of the paddles will be only equivalent to the friction of the 

 stream put in motion by their first action on it : and this effect is by far too small 

 to be obtained by a complicated arrangement, which it would be difficult to render 

 durable ; hence the construction is imperfect. 



The subject is further treated in the Appendix. 



