ARTICLES 271 



resistance to impact of A is only 3 per cent, of that of B. Steels 

 of certain compositions show the brittleness fully ; the rate of 

 cooling from the tempering temperature is the essential point ; 

 a steel which has become tough or brittle may by appropriate 

 re-treatment be rendered the reverse ; no structural change 

 has so far been observed between the brittle and tough states ; 

 and finally certain casts of steel can never be rendered tough 

 or others brittle. No explanation fully covering the facts has 

 yet been given. 



