ON PADDLE WHEELS. 145 



shafts farthest from the paddle wheels are fixed bevel wheels, which act upon each other, or 

 are both acted upon by an intermediate bevel wheel in connexion with the steam engine or 

 first mover. 



By this arrangement the surface of each float when under the centre is perpendicular to 

 the vessel's course, so that the whole pressure is at that moment effective, and, when over the 

 centre, it is parallel to the course of the vessel, so as to cause the least possible useless 

 resistance. 



The circumferential velocity of any given point of a float being V, and the velocity of the 



V 

 vessel v, the effective velocity of the given point when under the centre is v, which 



shows that the upper edge of the float would back water in the middle of the stroke, if the 

 ratio of the velocity of the vessel to the circumferential velocity of the inner edges of the floats 



exceeded 



It is already well established that the more the circumferential velocity of the floats of a 

 paddle wheel exceeds the speed of the vessel, the greater is the waste of power ; and Perkins's 

 wheel requires a rather large excess, so that this quality, together with the great weight of 

 the wheels compared with that of common wheels of equal effect, the use of bevel wheels to 

 turn the shafts, which must be longer than they usually are, and the inconvenient position of 

 the wheels, which makes it very difficult to support them, and exposes them very much to 

 the action of the winds and waves ; all these circumstances are so conclusive of the disadvan- 

 tage of the system, that it is unnecessary to carry the investigation any farther. An additional 

 argument against the utility of this wheel is, that it has not been adopted in practice. 



Several other varieties of paddle wheels with oblique floats have been invented and tried, 

 but without success, and, as there is neither ingenuity nor novelty of invention in any of 

 them, we shall pass them over. 



CLASS II. PADDLE WHEELS WITH FEATHERING FLOATS. 



This class may be subdivided into, 



A. Paddle wheels with floats turning on radial axes, and 



B. Paddle wheels with floats turning on horizontal axes or spindles. 



A. Paddle Wheels with floats turning on radial axes. 



Of these very little need be said, as they have not yet been, and are not likely ever to be, 

 adopted. The action of all of them is nearly the same : the floats either enter or leave the 

 water, or both, in the direction of their surface, or at a very acute angle with it. The action 

 is therefore generally very oblique ; besides which, the mode of feathering the floats is so 

 objectionable, that that alone would be sufficient to condemn the system. The floats are 

 fixed to spindles radiating from the axis of the wheel, each of which is furnished with a crank 

 at its inner extremity, through the medium of which the spindle is made to turn by means of 



