Square of the velocity of the stream
------------------------------------ ×
Twice gravity (64.33)
volume of water in cubic feet per second × 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
------ × 30 × 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 = 0.35½
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