his paper last year, for there are differences in the slips, the
proportions of blade area to disk, and, to some extent, in the shapes of
the blades, which are not taken into account in that method. Assuming,
however, as Mr. Froude does, a constant proportion of blade area to disk,
and a uniform pattern of blade, the determination of the diameter for a
given set of conditions may, as a rule, be a complete solution of the
problem of the design of a screw, but these assumptions do not cover all
the necessities of actual practice, which make it extremely desirable to
know something about the influence or efficiency of various proportions of
blade area to disk, and of the form or distribution of a given area.

During the discussion which followed, Mr. John said that, both as regarded
the mercantile marine and the Royal Navy, there were few data to work upon,
but few ships having been built with twin screws. Mr. Linnington's
proportions of pitch to diameter of 1.2 to 1.34 was not invariably adhered
to. He mentioned a couple of small twin screw vessels where the proportion
of pitch to diameter came nearly to 1.5, and he remembered a few years ago
the propellers in one of these vessels being changed and the pitch
increased, the result being a very considerable improvement. He believed
they might go with quick running twin screw engines to a larger proportion
of pitch to diameter than they could with a single screw. He might instance
the change in the Iris. She was first engined with the pitch equal to the
diameter, and she gained two knots or thereabout when the diameter was
reduced 2 ft. and the pitch increased 2 ft.

Admiral De Horsey said that he tried experiments with the single screw in
the Aurora. She had a feathering serew, and when the sails were used to
assist, they commonly altered the pitch of the screw according to the
strength of the wind. The screw could be altered while it was revolving,
and as the wind freshened they coarsened the pitch, and when they wanted to