ter than the
speed of the small vessel. If therefore the speed of the Fairy be 13 knots,
the speed of the new vessel will be 22.49 knots, although the proportion of
power to sectional area, which is supposed to be the measure of the
resistance, is in both cases precisely the same. If the speed of the Fairy
herself had to be increased to 22.29 knots, the power would have to be
increased in the proportion of the cube of 13 to the cube of 22.49, or 5.2
times, which makes the power necessary to propel the Fairy at that speed
equal to 624 nominal horses power.

STRUCTURE AND OPERATION OF PADDLE WHEELS.

551. _Q._--Will you describe the configuration and mode of action of the
paddle wheels in general use?

_A._--There are two kinds of paddle wheels in extensive use, the one being
the ordinary radial wheel, in which the floats are fixed on arms radiating
from the centre; and the other the feathering wheel, in which each float is
hung upon a centre, and is so governed by suitable mechanism as to be
always kept in nearly the vertical position. In the radial wheel there is
some loss of power from oblique action, whereas in the feathering wheel
there is little or no loss from this cause; but in every kind of paddle
there is a loss of power from the recession of the water from the float
boards, or the _slip_ as it is commonly called; and this loss is the
necessary condition of the resistance for the propulsion of the vessel
being created in a fluid. The slip is expressed by the difference between
the speed of the wheel and the speed of the vessel, and the larger this
difference is the greater the loss of power from slip must be--the
consumption of steam in the engine being proportionate to the velocity of
the wheel, and the useful effect being proportionate to the speed of the
ship.

552. _Q._--The resistance necessary for propulsion will not be situated at
the circumference of the wheel?

_A._--In the feathering wheel, where every part of any one immerged float
moves forward with the same horizontal velocity, the pressure or resistance
may be supposed to be concentrated in the centre of the float; whereas, in
the common radial wheel this cannot be the case, for as the outer edge of
the float moves more rapidly than the edge nearest the centre of the wheel,
the outer part of the float is the most effectual in propulsion. The point
at which the outer and inner portions of the float just balance one another
in propelling eff