l of which is a function of the travel of the bed
containing the model. With a pointer, which is connected by a system
of levers to the cutting tools, the operator traces out the water
lines upon the plan as the machine and its bed are in motion, with the
result that corresponding lines are cut upon the model. The cutting
tools are swiftly revolving knives which work on vertical spindles
moved in a lateral direction (brought near or removed from each
other), according to the varying breadth of the water lines throughout
the length of the model, as traced out by the operator's pointer. In
this way a series of longitudinal incisions are made on the model at
different levels corresponding to the water lines of the vessel. The
model is now taken from the bed of the machine and the superfluous
material or projection between the incisions is removed by means of a
spokeshave or other sharp hand tool, and the whole surface brought to
the correct form, and made fair and smooth.

To test accuracy of form, the weight of model is carefully taken, and
the displacement at the intended trial draught accurately determined
from the plan of lines. The difference between the weight of model and
the displacement at the draught intended is then put into the bottom
of the model in the form of small bags of shot, and by unique and very
delicately constructed instruments for ascertaining the correct
draught, the smallest error can at once be detected and allowed for.
The models vary in size from about one-tenth to one-thirtieth of the
size of the actual ship. A model of the largest size can be produced
and its resistance determined at a number of speeds in about two days
or so. The mode of procedure in arranging the model for the resistance
experiment, after the model is afloat in the tank at the correct
draught and trim, consists in attaching to it a skillfully devised
dynamometric apparatus secured to a lightly constructed carriage. This
carriage traverses a railway which extends the whole length of the
tank about 15 in. or 18 in. above the water. The floating model is
carefully guided in its passage through the water by a delicate
device, keeping it from deviating either to the right or left, but at
the same time allowing a free vertical and horizontal motion. The
carriage with the model attached is propelled by means of an endless
steel wire rope, passing at each end of the tank around a drum, driven
by a small stationary engine, fitted wi