OF ARTS AND SCIENCES. 323 



a gentle percussive action on a part of a bar, the metal becoming 

 changed at one point only, and hence — by chemical dissection the bar 

 being laid open — the fibrous metal could be seen united to that 

 changed portion, which had become highly crystalline and generally 

 brittle. 



" It is well known that the crystalline condition, assumed after the 

 iron has been laminated to the extent of rendering it uniformly fibrous, 

 is due to motion and change of place between the molecules of the 

 iron, without the condition of softening or fluidity. The extreme 

 cases often present us with a polarized condition, in which the crystal- 

 lized iron is as perfect indeed as would have resulted from cooling a 

 fluid mass in a state of repose. 



" Malleable iron in its fibrous arrangement may be assumed as 

 exhibiting its particles of broken-down crystals in a state of tension, 

 in which certain physical conditions, such as specific gravity and re- 

 sistance to strain, are insured while this state continues. A return to 

 the normal or crystalline state requires only vibratory motion, in aid 

 of natural polarizing forces always acting, to cause molecules to unite 

 into regular solids and pass to a condition of repose, in which the 

 masses become brittle. It is among the triumphs of modern science 

 that a successful effort has been made to overcome the practical disad- 

 vantages arising from this disposition in malleable iron to become 

 brittle ; and in one of its most important applications — that of rail- 

 way axles — this has been effected completely. The discovery by 

 E. M. Connell, an English engineer, that the vibrations among the 

 particles of hollow masses do not result in crystalline arrangements, 

 has led to the adoption of hollow axles, in which uniformity of thick- 

 ness of metal is insured, while only two thirds of the weight of the 

 metal used for forming a solid axle is retained. 



" An interesting case of the formation of large crystals under quite 

 new conditions, in an alloy of which zinc forms the larger part, has 

 recently been observed by me. This alloy, when rapidly cooled, 

 presents a crystalline arrangement much like that of steel. When 

 cast in the form of balls, in cold metallic moulds, it shows the effect 

 of chilling remarkably. The metal forming the exterior becomes 

 solid and more dense, while that in the interior conforming to it leaves 

 a void of a spherical form, in each ball of an inch in diameter as larse 

 as a small pea. From well-known facts, we should have expected to 

 find this cavity bounded by crystals or crystalline facets ; which does 



