Chap. 3.] Water Wheels* 469 



one- fifth greater in proportion to the velocity of the 

 fluid, than it would receive in an unconfined ftream, 

 becaufe in the latter cafe the water which abounds is 

 turned behind the float, and refifts it; on the contrary, 

 when rhe wheel moves in a frame, there is only a fmall 

 quantity of water, which moves with as much velocity, 

 or with rather more, than the float- board. 



It has been proved by experience, that when this 

 cafe or frame is but juft wide and deep enough to 

 admit the wheel to move freely, and the water has 

 an opportunity of running out after having given its 

 fhock or impulfe, the direct and perpendicular force 

 againfl the floats of the wheel is about twice the force 

 which the float would receive if it was plunged to the 

 fame depth in an unconfined current. 



When a wheel furnimed with forty -eight floats turns 

 in a cafe or frame, and it is not plunged very deep in 

 the water, its circumference will have about two-fifths 

 of the velocity of the .current, in which cafe the ma- 

 chine will produce the greateft effect. 



It appears that float-boards are the moft advan- 

 tageous when they are placed in a direct line towards 

 the center of the wheel j becaufe but few of them 

 would be required, fmce they would then be flruck 

 perpendicularly by the water, which produces the mod 

 powerful effect, When they incline, the mock is 

 oblique, which diminifhes the effort j yet a certain 

 degree of inclination caufes the water to rife the 

 length of the float, and to remain there a certain time ; 

 it then acts by its gravity after having acted by its 

 fhock or fall, and the effect which refults from this 

 arrangement more than compenfates for the diminu- 

 tion which the Ihock fuffered from the obliquity with 

 which the force was applied in the firft inftance. Jn 

 general, thp wheels placed in frames which have a cer- 

 H h 3 Sain, 



