v^ction of Iron in motion on Tempered Steel. 326 



"vfras set with small particles of steel, which, seen through a 

 lens, did not appear as if untempered, and which^ when tried 

 with a file, were found as hard as the best tempered steel. 

 Suspecting, therefore, some other cause for the effect, they 

 .first endeavoured to ascertain what degre<3 of m'otion was 

 sufiicient, simply to compensate for the power whicii m ordi- 

 nary circumstances steel has of cutting iron, and above which 

 iron, on the contrary, becomes possessed of the power oif 

 cutting steel. 



The steel 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 de;iree of velocity could be given to it. The 

 lime was measured by a temporary pendulum. Whilst the 

 velocity of the iron wheel, measured at its circumference, 

 was less than 34 feet in a second, the 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 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 incieased con- 

 tinually with the velocity ; and at 70 fi'et per second, only 

 imperceptible jiortions of iron could be detached, whilst the 

 gravers were attacked with the greatest violence. 



Having ascertained the point at which the change in the 

 reciprocal action of iron and steel took place, the next thing 

 was to ascertain whether the softening of the steel was the 

 necessary cause The wlie<^l was therefore cleared of the 

 particles of steel at its edge, and put it into motion with ve- 

 locities from 40 to 200 feet prr second ; the gravers were 

 then appli> d to it for an instant only at a time, and though 

 sensibly attacked by the iron, yet not the slightest softening 

 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 liave been heated, thoug^h the neifrhbonrinir particles jvcrc 

 not. — Ed. Land. Joitr. 



