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548. *Q.*—These experiments, you have
already stated, were all made on paddle vessels.
Have similar coefficients of performance been obtained
in the case of screw vessels?

*A.*—The coefficients of a greater
number of screw vessels have been obtained and recorded,
but it would occupy too much time to enumerate them
here. The coefficient of performance of the Fairy
is 464.8; of the Rattler 676.8; and of the Frankfort
792.3. This coefficient, however, refers to nautical
and not to statute miles. If reduced to statute
miles for the purpose of comparison with the previous
experiments, the coefficients will respectively become
703, 1033, and 1212; which indicate that the performance
of screw vessels is equal to the performance of paddle
vessels, but some of the superiority of the result
may be imputed to the superior size of the screw vessels.

INFLUENCE OF THE SIZE OF VESSELS UPON THEIR SPEED.

549. *Q.*—Will large vessels attain
a greater speed than small, supposing each to be furnished
with the same proportionate power?

*A.*—It is well known that large vessels
furnished with the same proportionate power, will
attain a greater speed than small vessels, as appears
from the rule usual in yacht races of allowing a certain
part of the distance to be run to vessels which are
of inferior size. The velocity attained by a
large vessel will be greater than the velocity attained
by a small vessel of the same mould and the same proportionate
power, in the proportion of the square roots of the
linear dimensions of the vessels. A vessel therefore
with four times the sectional area and four times the
power of a smaller symmetrical vessel, and consequently
of twice the length, will have its speed increased
in the proportion of the square root of 1 to the square
root of 2, or 1.4 times.

550. *Q.*—Will you further illustrate
this doctrine by an example?