l the special and highly ingenious
instruments and appliances which the scientific skill of the late Dr.
Froude brought into existence, and have been since his day improved
upon by his son, Mr. R. E. Froude, and other experts.

Through the courtesy of our own Admiralty and of Messrs. Denny, of
Dumbarton, the Italians have been permitted to avail themselves of the
latest improvements which experience has suggested, and the
construction of the special machinery and apparatus required has been
executed by firms in this country having previous experience in this
connection--Messrs. Kelso & Co., of Commerce Street, Glasgow; and Mr.
Robert W. Munro, of London.

Having briefly traced the origin and development of the system of
model experiment, it may now be of interest to describe the _modus
operandi_ of such experiments, and explain the way in which they are
made applicable to actual ships. The models with which experiments are
made in those establishments conducted on the lines instituted by Mr.
Froude are made of paraffin wax, a material well adapted for the
purpose, being easily worked, impervious to water, and yielding a fine
smooth surface. Moreover, when done with, the models may be remelted
for further use and all parings utilized. They are produced in the
following manner: A mould is formed in clay by means of cross sections
made somewhat larger than is actually required, this allowance being
made to admit of the cutting and paring afterward required to bring
the model to the correct point. Into this mould a core is placed,
consisting of a light wooden framework covered with calico and coated
with a thick solution of clay to make it impervious to the melted
paraffin. This latter substance is run into the space between the core
and the mould and allowed to cool. This space, forming the thickness
of the model, is usually from 3/4 in. for a model of 10 ft. long to 11/4
in. and 11/2 in. for one of 16 ft. and 18 ft. long. When cold, the model
is floated out of the mould by water pressure and placed bottom upward
on the bed of a shaping machine, an ingenious piece of mechanism
devised by the late Dr. Froude, to aid in reducing the rough casting
to the accurate form. The bed of this machine, which travels
automatically while the machine is in operation, can be raised or
lowered to any desired level by adjusting screws. A plan of water
lines of the vessel to be modeled is placed on a tablet geared to the
machine, the trave