hardening and tempering; for example, as dies, tools of various
description, sword blades, and thin plates rolled at a low temperature
or subjected to cold hammering. In the foundry the appearance of
internal stresses is of still more frequent occurrence. The neglect of
certain practical rules in casting, and during the subsequent cooling,
leads to the spontaneous breakage of castings after a few hours or days,
although taken out of the sand apparently perfectly sound. Projectiles
for penetrating armor plate, and made of cast steel, as well as shells
which have been forged and hardened, and in which the metal possessed an
ultimate resistance of over twelve thousand (12,000) atmospheres, with
an elastic limit of more than six or seven thousand atmospheres, will
crack to a serious extent, and even break up in the lathe, while the
recess for the copper ring is being turned out. In shell of this nature,
as well as in chilled cast iron shell, the heads are apt to fly off
spontaneously either while they are lying in store or during transport.
Such phenomena, it seems to me, demonstrate the existence of internal
stresses of considerable magnitude in the metal of the projectiles, and
it is highly probable that the manufacture of many articles would have
approached nearer to perfection had more attention been bestowed upon
the study of the internal stresses which they were liable to. Having
thus explained the nature and importance of the subject, I will proceed
to describe the experiments which I have made with a view to its
illustration.--_London Engineer._

* * * * *




ELEMENTS OF ARCHITECTURAL DESIGN.[1]