1146

THEORY AND PRACTICE OF ENGINEERING.

Book 11.

number of floats. In the close canal, he made use of a wheel the extreme diameter ofwhich was 3 feet 1 *87 inches, 5 inches in breadth, and the depths of the float-boards from4 to 5 inches: the axis of the wheel which received the cord was 2 inches in diameter; thediameter of the pulley 3$ inches. The wheel was suspended on its axis within half a lineof the bottom of the canal: the sluice was raised 1 inch, and the velocity of the streamwas 300 feet in 33 seconds: in a close canal, the effect was with 48 floats on a wheel of3 feet 1*87 inches diameter greater than that with a less number: the arc immersed wasabout T ' 3 of the circumference of the wheel.

Water-wheels used in rivers have a less number of float-boards, and in the next experi-ment the wheel was 3 feet diameter, breadth 6 inches, and the depth of the float-boards 6inches, the whole weight of the moving parts of the apparatus being 44 lbs.

The stream was open, 12 or 13 feet wide, and 7 or 8 inches deep, and the float-boardswere immersed 4 inches: the wheels had a variety of float-boards, that with 48 producingvery little more effect than one with half that number; but there was considerabledifference between those with 24 and 12, the former being decidedly preferable: it wasapparent, when the wheel dipped § of its circumference, less than 24 ought not to beused.

In the close canal the. sluice was raised 2 inches, the velocity of the current 300 feet in27 seconds, and 48 float-boards to the wheel; and trials were made with the same wheels,the maximum effect of which was 34^ lbs., raised by 20 T 3 3 turns of the wheel in 40 seconds,thus making the product of the weight raised 704^ lbs. The velocity of the current wasto the velocity of the outer circumference of the wheel, as 10 is to 4-32 when the power isa maximum.

In the open stream, where the velocity of the current was 68J inches per second, thefloat-boards dipping 4 inches in the water, the wheel having 24 float-boards, the maximumeffept was 60 lbs. weight raised, 11| being the number of turns of the wheel in 40 seconds,and 710 the product of the weight by the number of turns. The velocity of the currentwas to the velocity of the outer edge of the float-boards at the maximum, as 10 is to 4*9nearly. The velocity of the wheel in the stream and in the canal was nearly the same.The greatest effect, as it appears from Bossut’strials, was obtained when the inclination ofthe floats to the radius was from 15 to 30degrees.

Construction of Undershot Wheels _ The wheel

here represented has twenty-four float-boards ;c d is that receiving the impulse of the water,which, in consequence of falling from a height,moves with great velocity down the inclinedmill-course M N, the construction of whichrequires the greatest consideration, as does thenumber, form, and position of the float-boards,and the velocity of the wheel, in relation tothat of the water, when the effect is a max-imum : it being important to have the heightof the fall as great as possible, the canal ordam which conducts the water from the headshould not have more inclination than is abso-lutely necessary; an inch in 200 yards is con-sidered sufficient, carebeing taken to make thedeclivity for the first 50yards about £ inch, thatthe water may have suffi-cient velocity to preventits running back into thehead.

The inclination of thefall, shown by the angleCGR, should be 25° 50 / ,or C R; the radius shouldbe to C R, the tangent ofthe angle, as 25 to 12 ; andsince the surface of thewater S6 is bent from ahinto ac before it is pre-cipitated down the fall,it will be necessary to

Fig.1736.

UNDERSHOT WHEEL.

Fig. 1736.

UNDERSHOT WHEEL.