water discharged under
pressure, more particularly in the hope that, as water power is extremely
abundant in Canada, any remarks relating to the subject may not fail to
prove interesting.

Between the action of turbines and that of screw propellers exists an exact
parallelism, although in one case water imparts motion to the buckets of a
turbine, while in the other case blades of a screw give spiral movement to
a column of water driven aft from the vessel it propels forward. Turbines
have been driven sometimes by impact alone, sometimes by reaction above,
though generally by a combination of impact and reaction, and it is by the
last named system that the best results are now known to be obtained.

The ordinary paddles of a steamer impel a mass of water horizontally
backward by impact alone, but screw propellers use reaction somewhat
disguised, and only to a limited extent. The full use and advantages of
reaction for screw propellers were not generally known until after the
publication of papers by the present writer in the "Proceedings" of the
Institution of Naval Architects for 1867 and 1868, and more fully in the
"Transactions" of the Society of Engineers for 1868. Since that time, by
the author of these investigations then described, by the English
Admiralty, and by private firms, further experiments have been carried out,
some on a considerable scale, and all corroborative of the results
published in 1868. But nothing further has been done in utilizing these
discoveries until the recent exigencies of modern naval warfare have led
foreign nations to place a high value upon speed. Some makers of torpedo
boats have thus been induced to slacken the trammels of an older theory and
to apply a somewhat incomplete form of the author's reaction propeller for
gaining some portion of the notable performance of these hornets of the
deep. Just as in turbines a combination of impact and reaction produces the
maximum practical result, so in screw propellers does a corresponding gain
accompany the same construction.

[Illustration: FIG. 1.]

[Illustration: FIG. 2.]

_Turbines_.--While studying those effects produced by jets of water
impinging upon plain or concave surfaces corresponding to buckets of
turbines, it simplifies matters to separate these results due to impact
from others due to reaction. And it will be well at the outset to draw a
distinction between the nature of these two pressures, and to remind
ourselves of th