Mechanical Science, 8fc. 101 



of velocity could be given to it. The time was measured by a 

 temporary pendulum. Whilst the velocity of the iron wheel, mea- 

 sured 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 9 inches, it was 

 slightly attacked, and the iron turnings cut by it were less abund- 

 ant. At 35 feet 1 inch, the effect of the iron on the steel was very 

 decided. Above this point the difference increased continually 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 in the reci- 

 procal action of iron and steel took place, the next thing was to 

 ascertain whether the softening of the steel was the necessary 

 cause. The wheel was therefore cleared of the particles of steel at 

 its edge, and put into motion with velocities from 40 to 200 feet 

 per second ; the gravers were then applied 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 con- 

 tinued, then the gravers became hot and were softened ; but the 

 fracture of the steel was then very different to the fracture of the 

 tempered portion, and the steel, when applied to the wheel would 

 give way before it, forming a bur : the action of the iron also on 

 it seemed rather diminished than otherwise. 



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 awheel of soft iron, moving 

 at velocities from 130 to 200 feet per second : the first was acted 

 upon, but the surface produced was unequal and rough ; the agate 

 was also acted upon though less powerfully : but it is supposed that 

 this means, even when much greater velocities are used, cannot 

 be applied to the cutting of these or similar substances with advan- 

 tage ; at the same time the effects, though small, confirm the au- 

 thors in their view of the cause of the phenomenon. 



They then quote 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, 



• This roasoninj: is /hardly conclusive, since the particle removed might 

 have been heated, tliou;^li the nei;;iibouiing particles were not. — E. 



Vol.. XVIII. M 



