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.--_Neuste Erfindungen und Erfahrungen_.

* * * * *




TAR FOR FIRING RETORTS.


The attention of gas engineers has been forcibly directed to the use of tar
as a fuel for the firing of retorts, now that this once high-priced
material is suffering, like everything else (but, perhaps, to a more marked