(1) The development of heat depends on the form of the faces and the energy of the blow.

(2) In the case of faces with sharp edges, the process described allows this heat to be clearly indicated.

(3) The development of heat is greatest where the shearing of the material is strongest.  This shearing is therefore the mechanical cause which produces the heating effect.

(4) With a blow of sufficient energy and a bar of sufficient size, about 80 per cent. of the energy reappears in the heat.

(5) The figures formed by the melted wax give a sort of diagram, showing the distribution of the heat and the character of the deformation in the bar.

(6) Where the energy is small the calculation 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.