526 Action of Iron in motion on Tempered Steel. 
of the iron also on it seemed rather diminished than other~ 
wise. 
Hence MM. Darier and Colladon conclude that the effect 
was not due to the softening of the steel; nor, as the wheel 
was clean, could it be due to the particles of steel adhering 
to its surface ; and they feel inclined to attribute it to the 
blow only, thinking it easy to conceive that the fragile steel 
may be broken by the action of the iron before it can have 
time to introduce itself between its molecules. 
Rock crystal and agate were held to a wheel of soft iron, 
moving at velocities from 130 to 200 feet per second: the 
& Ww 
rough; the agate was also acted upon though less power- 
ly : bat it is supposed that this means, even when much 
greater velocities are used, carinot be applied to the cutting 
of these or similar substances with advantage; at the same 
time the effects, though small, confirm the authors in their 
view of the cause of the phenomenon. 
They then quofe similar effects known to be due to the 
force of percussion, as the piercing of a plank by a ball of 
tallow, the force of liquids, even when moving with great 
velocity : when, therefore, to an edge of soft iron, moving 
with the velocity described, hard elastic bodies are applied, 
as steel, agate, &c., their particles are displaced and torn off, 
for they cannot move by each other without division; but 
when a soft body is applied to the wheel, as copper, brass, 
tin, and even soft steel, then the substance is pressed before 
the iron, and being ductile rises up in burs. 
The iron wheel was replaced by one composed of 4 cop- 
per; 1 tin; but this hard and elastic alloy slipped over the 
violent vibrations. A wheel of copper was then used; steel 
gravers constantly cut this wheel without being touched by it: 
but when gravers were made of alloys, all harder than cop- 
per but softer than steel, the copper wheel’immediately at- 
tacked them. Hence it appears that a small difference in 
with the substances that were attacked by the wheel. The 
authors conclude by stating their opinion, that the experi- 
