ON PADDLE WHEELS. 



153 



this line is constantly changing its position, the cranks must be set at different angles with 

 the surface of their respective floats, in order that the latter may all have the same inclination 

 when at the same point of the circumference. Fig. 1. PI. LXXVII. will explain this arrange- 

 ment : C is the centre of the wheel, and E that of the guiding frame, r r r the radii or arms ; 

 the polygon, or outer frame of the wheel, F F F, is made sufficiently large to include the whole 

 of the floats, in order to have a bearing for cross-stays, which traverse the wheel from one 

 side to the other at the points F F F, &c. ; S, S, S, &c., are the spindles with the cranks 

 S G, S G, S G, &c., exactly as in Buchanan's wheel, except that each crank, S G, makes an 

 angle with its float, differing from that of the next on either side by half the angle included 

 between the respective arms of the wheel ; ff,g,ff, &c., are the arms, and G, G, G, the periphery 

 of the guiding frame. The positions of the paddle-cranks are easily found by drawing the 

 wheel without the floats with the guiding frame in any arbitrary position (in the figure its 

 centre is immediately over the shaft, but any other position would do as well) ; the line C E 

 being given, all the cranks must be parallel to it, and the floats radiate from the highest point 

 of the circumference which passes through the spindles ; each float being then fixed to its 

 crank, will evidently radiate from the same point during the whole of every revolution of the 

 wheel, and its inclination will consequently always be half that of the radius. 



The action of this wheel is theoretically very good, the pressure on the floats being nearly 

 uniform throughout the stroke ; but the great friction, liability to get out of order, and other 

 difficulties attending its construction, have hitherto overbalanced its theoretical advantages. 

 The wheel represented in the figure is of the same dimensions as those in the preceding plates, 

 and the same speed and number of revolutions in each of the Figures 2 and 4, as in the 

 corresponding figures in the other plates. In 

 comparing the nodes, Figs. 3 and 5, with those 

 of the other wheels shown in Plates LXXIV., 

 LXXV., LXXVI., the superiority of Oldham's 

 wheels is manifest : the float strikes the water, 

 on entering, less violently than that of the 

 common wheel, having at that moment less 

 effective velocity, and there is throughout less 

 loss from oblique action, from its inclination 

 being always less : the whole immersed surface 

 of the float is always effective, which gives it 

 another advantage over the divided float of 

 Field's wheel; and the radius of the rolling 

 circle is not limited, as with Buchanan's, which 

 causes a great proportion of the power to be 

 spent simply in turning the wheels. 



To investigate the action of the floats, let 

 L L be the water line, C the centre of the 

 wheel, S' S" its vertical diameter, C S one of 

 the radii, A B the float, and S the spindle. 

 Let R = the radius C S ; / = AS, the half 

 depth of the float. Produce A B until it meet 



r 



