hat the cost in screw steamers is about one third less than in the sailing
ships; the greater expedition of the screw steamers much more than
compensating for the expense which the maintenance of the machinery
involves.

SCREW AND PADDLES COMBINED.

613. _Q._--Would not a screw combined with paddles act in a similarly
advantageous way as a screw or paddles when aided by the wind?

_A._--If in any given paddle vessel a supplementary screw be added to
increase her power and speed, the screw will act in a more beneficial
manner than if it had the whole vessel to propel itself, and for a like
reason the paddles will act in a more beneficial manner. There will be less
slip both upon the paddles and upon the screw than if either had been
employed alone; but the same object would be attained by giving the vessel
larger paddles or a larger screw.

614. _Q._--Have any vessels been constructed with combined screw and
paddles?

_A._--Not any that I know of, except the great vessel built under the
direction of Mr. Brunel. The Bee many years since was fitted with both
screw and paddles, but this was for the purpose of ascertaining the
relative efficiency of the two modes of propulsion, and not for the purpose
of using both together.

615. _Q._--What would be the best means of accelerating the speed of a
paddle vessel by the introduction of a supplementary screw?

_A._--If the vessel requires new boilers, the best course of procedure
would be to work a single engine giving motion to the screw with high
pressure steam, and to let the waste steam from the high pressure engine
work the paddle engines. In this way the power might be doubled without any
increased expenditure of fuel per hour, and there would be a diminished
expenditure per voyage in the proportion of the increased speed.

616. _Q._--What would the increased speed be by doubling the power?

_A._--The increase would be in the proportion of the cube root of 1 to the
cube root of 2, or it would be 1.25 times greater. If, therefore, the
existing speed were 10 miles, it would be increased to 12-1/2 miles by
doubling the power, and the vessel would ply with about a fourth less coals
by increasing the power in the manner suggested.

617. _Q._--Is not high pressure steam dangerous in steam vessels?

_A._--Not necessarily so, and it has now been introduced into a good number
of steam vessels with satisfactory results. In the case of locomotive
engines, where it