lculation of the percentage is not
reliable.

So far we have spoken only of cases where the anvil and monkey have
sharp faces. Where the faces are rounded the phenomena are somewhat
different. Figs. 7 to 12 give the area of melted wax in the case of bars
struck with blows gradually increasing in energy. It will be seen that,
instead of commencing at the edges of the indent, the fusion begins near
the middle, and appears in small triangular figures, which gradually
increase in width and depth until at last they meet at the apex, as in
Fig. 12. The explanation is that with the rounded edges the compression
at first takes place only in the outer layers of the bar, the inner
remaining comparatively unaffected. Hence the development of heat is
concentrated on these outer layers, so long as the blows are moderate in
intensity. The same thing had already been remarked in cases of holes
punched with a rounded punch, where the burr, when examined, was found
to have suffered the greatest compression just below the punch. With
regard to the percentage of energy developed as heat, it was about the
same as in the previous experiments, reaching in one case, with an iron
bar and with an energy of 110 kilogram-meters, the exceedingly high
figure of 91 per cent. With copper, the same figure varied between 50
and 60 per cent.--_Iron_.

* * * * *

A NOVEL PROPELLER ENGINE.

By Prof. C.W. MacCord.

The accompanying engravings illustrate the arrangement of a propeller
engine of 20 inch bore and 22 inch stroke, whose cylinder and valve gear
were recently designed by the writer, and are in process of construction
by Messrs. Valk & Murdoch, of Charleston, S.C.

In the principal features of the engine, taken as a whole, as will be
perceived, there is no new departure. The main slide valve, following
nearly full stroke, is of the ordinary form, and reversed by a shifting
link actuated by two eccentrics, in the usual manner; and the expansion
valves are of the well known Meyer type, consisting of two plates on the
back of the main valve, driven by a third eccentric, and connected by a
right and left handed screw, the turning of which alters the distance
between the plates and the point of cutting off.

The details of this mechanism, however, present several novel features,
of which the following description will be understood by reference to
the detached cuts, which are drawn upon a larger scale than