6’ x 5’       2
-------  x 2.5  = 0.468
400

[TEX:  \frac{6’ \times 5’}{400} \times 2.5^2 = 0.468]

horse power of the wheel.

The total power of the stream due to the area of the blade equals the

Square of the velocity of the stream
------------------------------------ x
Twice gravity (64.33)

volume of water in cubic feet per second x 62.5 (weight of 1 C’) = the value or gross effect in pounds falling 1 foot per second.  This sum divided by 550 = horse power.  Thus, as per last example,

2
5
------ x 30 x 62.5
64.33
---------------------- = 1.32 the horse power of the current
550

[TEX:  \frac{\frac{5^2}{64.33} \times 30 \times 62.5}{550} = 1.32 \text{ the horse power of the current}]

due to the area of the blades of the water wheel.

For the efficiency of this class of wheel, with slightly curved and thin blades, divide the horse power of the wheel by the horse power of the current area, equals the percentage of efficiency.

As in the last case,

  0.468 / 1.32 = 0.351/2

per cent. efficiency of the water wheel.

With higher velocities of stream and wheel the efficiency will be from 2 to 3 per cent. less, although the horse power will increase nearly with the increase in velocity of the current.

For details of application of various forms of current wheels for power purposes see illustrated description Yagn’s and Roman’s floating motors in SCIENTIFIC AMERICAN SUPPLEMENT, No. 463.

A very good example of a floating motor of the propeller class is Nossian’s fluviatile motor, illustrated and described in SCIENTIFIC AMERICAN SUPPLEMENT, No. 656.

[Illustration:  Fig. 24.]

Fig. 24 represents a very complete floating motor, in which the floats are wedge shaped at the stem, for the purpose of increasing the current between them, the wheel being an ordinary current wheel, as shown in Fig. 23, with a curved shield or gate in front, which can be moved around the periphery of the wheel for the purpose of regulating its speed or stopping its motion by cutting off the stream from the buckets.

The float, rising and falling with the stream, is held in position by a braced frame swinging on anchorages within the mill on shore, and parallel with a swiveled shaft.

Tide wheels and tidal current wheels have been in use for more than 800 years, and were largely in use in Europe and the United States during the first half of the present century.  No less than three were running in the immediate vicinity of New York, in 1840, for milling purposes.

Their day seems to be past, except in some special localities.  We will also pass them, and illustrate some of the

SELF-ACTING WATER-RAISING DEVICES.