FEATHERING PADDLE WHEELS.   211

is the resultant, and the plane of the float must contain P R.
Produce, R P, to cut the vertical through the centre, C, in, A,
and at right angles to the line, R A<sub>1</sub> (which is the line of the
float); layoff, H G, equal to the distance from the face of the
float to the centre of the hinge, and, G L, equal to the length of
the lever. Now set off in outline another float immediately
under the centre of the wheel, with its face perpendicular to the
surface of the water, and having the end of its lever at M.
With, M, and, L, as centres, and radius equal to, G C, describe
arcs intersecting at, E, then, E, is the centre of the eccentric
pin. Having thus determined the position of, E, the complete
wheel may be drawn down and the proper pitch given to the
floats. In practice, it is usual, instead of compounding the
velocities in the manner described, to place the eccentric pin in
such a position that the directions of the faces of the floats (while
they are passing through the water), if produced, shall meet in 
the point, A<sub>1</sub>, which is the intersection of a vertical line through
the centre, C, with the circle, which passes through the pivots
or hinges of the floats.

The feathering paddle-wheel, although much more efficient
than the radial wheel, is more liable to derangement, since any 
accident to the feathering apparatus would paralyse the action or
the entire wheel. For this reason it did not find general favour
when first introduced, but now it is almost universally adopted.
It requires to be made specially strong, and all the pins and
wearing parts should be cased with brass to prevent corrosion.
The boss or eccentric, E, which carries all the rods for feathering
the floats, runs loose on the fixed eccentric pin, and is turned
round by one specially strong rod, known as the driving or king
rod, shown at L E. The floats for large paddle-wheels are now
frequently made of steel and curved slightly concave, ) -> [two em right arrow]
towards the direction of meeting the water when steaming
ahead.