play. Of course, there are forces which war against the attainment of
the full extent of this advantage, viz., the greater condensation in the
cylinders and loss in the receiver or passages.

In regard to the former, it may be questioned whether by steamjacketing
the high pressure cylinder, correctly proportioning the steam passages,
and giving a due amount of compression in both cylinders, this may not
be reduced far below the generally received notion; and the latter cause
of loss may be considerably reduced in its effect by a more carefully
chosen cylinder ratio. The ratio usually adopted, between 3.5 and 4 to
1, whether the pressure be 70 lb. or 90 lb., may well be questioned.
With a cylinder ratio of 2.95 to 1, the economic performance is very
good, and equal to any with the higher ratio. A lower cylinder ratio has
another advantage of considerable value, viz., that the working pressure
can be much reduced as the boilers get older, while by giving a greater
amount of steam the power may be maintained--at an extra cost of steam,
of course, but not so great a cost as with higher ratios. The cut-off
in the high-pressure cylinder usually takes place at about 0.6, and
the ratio of expansion has decided the ratio of cylinders. The use of
separate starting valves in both cylinders obviates that necessity.

The difficulties in the way of taking advantage of the higher economic
properties of greater pressures than hitherto used on board ship, are,
it is submitted, not insuperable, and it would be to the interest of all
that they should be firmly and determinedly met. It may be accepted as
an average result that the Woolf engine, as usually arranged, will use
10 per cent. more steam than the receiver engine for the same power.

Of the three-cylinder receiver type the data are insufficient to form a
definite opinion upon; but so far the general working of the Arizona is