or leather; a_{1} is fixed to the wood, a_{2} is of metal, and, like
the movable block of a slide gauge, moves along A. In the same plane is a
second rod, perpendicular to A, and attached thereto, which is perforated
by a number of holes. A revolving pin, C, is adapted to pass through these
holes, to which a socket, D, is pivoted, C acting as its axis. To prevent
this pin from falling out, it is secured by a nut behind the rod. Through
the socket, D, runs a rod, E, which carries the guide point, s_{1}, and
pencil, s_{2}. Over s_{1} a rubber band is stretched, to prevent injury to
the varnish of the boat. Back of and to A and B a drawing board is
attached, over which a sheet of paper is stretched.

[Illustration: THE FRAME TRACER.]

The method of obtaining a section line is as follows: The rod, A, is placed
across the gunwale and perpendicular to the axis of the boat, and its
anterior vertical face is adjusted to each frame of the boat which it is
desired to reproduce. By means of the brackets, a_{1} and a_{2}, A is fixed
in place. The bolt, C, is now placed in the perforations already alluded
to, which are recognized as most available for producing the constructional
diagram. At the same time the position of the pencil point, s_{2}, must be
chosen for obtaining the best results.

Next the operator moves along the side of the boat the sharpened end,
s_{1}, of the rod, E, and thus for the curve from keel to gunwale, s_{2}
describes a construction line. It is at once evident that a_{2}, for
example, corresponds to the point, a_{1}. The apparatus is now removed and
placed on the working floor. If, reversing things, the point, s_{1}, is
carried around the construction curve, the point, s_{2}, will inscribe the
desired section in its natural dimensions. This operation is best conducted
after one has chosen and described all the construction curves of the
boat. Next, the different section lines are determined, one by one, by the
reversed method above described. The result is a half section of the boat;
the other symmetrical half is easily obtained.

If the whole process is repeated for the other side of the boat, tracing
paper being used instead of drawing paper, the boat may be tested for
symmetry of building, a good control for the value of the ship. For
measuring boats, as for clubs and regattas, for seamen, and often for the
so-called _Spranzen_ (copying) of English models, my apparatus, I doubt
not, will be very useful