Action of Iron in motion on T'empered Steel. 325 
was set with small particles of steel, which, seen through a 
a did not appear as if untempe ered, and which, when tried 
with a file, were found as hard as the best tempered steel. 
higsieat therefore. some other cause for the effect, they 
first endeavoured to ascertain what degree of motion was 
sufficient, simply to compensate for the power which in ordi- 
nary circumstances steel has of cutting iron, and above which 
iron, on me contrary, becomes possessed of the power of 
cutting s 
he neal employed consisted of gravers, very carefully 
tempered. The soft iron plate used was 7 inches 5 lines in 
diameter, and very carefully centred and mounted, so that 
any required degree of velocity could be given to it. The 
time was measured by a temporary pendulum. Whilst the 
velocity of the iron wheel, measured at its circumference, 
was less than 34 feet ina second, t e graver cut it with the 
greatest facility, and without any appearance of re-action. 
At 34 feet 5 inches, the graver did not cut the iron so well, 
but was itself unaffected. At 34 feet 9 inches, it was slightly 
attacked, and the iron turnings cut by it were less abundant. 
At 35 feet 1 inch, the effect of the iron on the steel was very 
decided. Above this point the difference increased con- 
tinually with the velocity ; and at 70 feet per second, only 
imperceptible portions of iron could be detached, whilst the 
gravers were attacked with the greatest violence 
Having ascertained the point at which the change i in the 
reciprocal action of iron and steel took place, the next thing 
was to ascertain W perks ihe 2 softening of the steel. was. the 
necessary cause. The was therefore cleared of the 
ough 
sensibly attacked by the iron, yet not the slightest acces 
could be observed.* When preserved wet, the effect was 
the same. When the pressure was strong and continued, 
then the gravers became hot and were softened ; but the 
fracture of the steel was then very different from the fracture of 
the tempered portion, and the steel, when applied to the 
wheel, would give way before it, forming a bur: the action 
*This reasoning is hardly conclusive, since the particle removed 
might have geo eats though the neighbouring particles were 
not.—Ed: Lond. 
