ps and of their engines, little or nothing has been done in
the way of improving the screw propeller. As a general rule it would
appear to be taken for granted that no radical improvement could be
made in the form of the propeller, although various metals have been
introduced in its manufacture with the view of increasing its
efficiency. For sea-going steamers, however, the shape remains the
same, the variation chiefly relating to the number of blades employed.
A striking departure from ordinary practice, however, has of late been
made by Mr. B. Dickinson, who has invented a screw propeller which, on
practical trial, has given an efficiency far in advance of the
ordinary screw. This new propeller we illustrate here in Figs. C and
D, while Fig. A shows an ordinary propeller. The Dickinson propeller
illustrated has six blades, giving a surface of 30 square feet; it is
right handed, and has pitch of 15 ft. and a diameter of 10 ft. 6 in.
The ordinary screw propeller shown at Fig. A is right handed and two
bladed, with a pitch at the boss of 13 ft. 6 in. and at the tip of 15
ft. It has a diameter of 10 ft. 9 in. and 32 square ft. of surface.
The projected area looking forward is 22 square ft. and the projected
area looking athwartship 22.84 square feet. The most graphic way of
illustrating the principle of Mr. Dickinson's propeller is to take a
two bladed propeller of the ordinary type as shown at Fig. A in the
annexed cuts, and divide into three sections as in Fig. B, then move
section No. 1 to the line position on the shaft of No. 3, and No. 3 to
that of No. 1, No. 2 remaining stationary. The effect of this
interchange will be that (having regard to the circle of rotation) No.
3, the rearmost section, will rotate in advance of No. 2, and No. 2 in
advance of No. 1 (see Fig. C). By this arrangement the water operated
on escapes freely astern from every blade--that from No. 1 passing in
the wake of No. 2, while that from Nos. 2 and 1 passes in the wake of
No. 3. Fig. D represents the blades with a wider spread as practically
used. The advantages claimed by Mr. Dickinson for his propeller, and
which are sufficiently important to be given in detail, are:

[Illustration: Figs. A-D.]

1. That the blades of each section, when the vessel is in motion,
necessarily cut solid, undisturbed water, each blade operating upon
precisely the same quantity of water as an individual broad blade
would do, though, of course, it parts with it in