MECHANICS AND USEFUL ARTS. 59 



are insured while this state continues. A return to the moral 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 over- 

 come the practical disadvantages arising from this disposition in malleable 

 iron to become brittle ; and in one of its most important applications 

 that of rail-way axles this lias been effected completely. Tnc discovery 

 by E. M. Connel, an English engineer, that the vibrations among the par- 

 ticles of hollow masses do not result in crystalline arrangements, has led 

 to the adoption of hollow axles, in which uniformity of thickness of metal 

 is insured, while only two thirds of the weight of the metal used for form- 

 ing 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 crys- 

 talline 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 large as a small pea. From well-known facts, 

 we should have expected to find this cavity bounded by crystals or crystal- 

 line facet', which does not occur; but its inner surface always exhibits the 

 flaws and irregularities observed when a metallic mass contracts in cooling 

 from a fluid state. These balls were used for reducing saline bodies to 

 powder in revolving cylinders containing several hundreds of them, and 

 the conditions were such that the balls, impinging on each other at mere 

 points as it were, received light blows over every part of their surfaces. 

 It would perhaps be inferred that the diameters would have been reduced 

 by the metal being forced into the void space as the effect of percussion. 

 Instead of this reduction, the balls first become elongated pear-shaped, they 

 then exhibited protuberances, and finally an elongated mammillary form, 

 in which the diameter was one half longer than that of the original, while 

 the whole bulk was increased from one to one and twenty-four hun- 

 dredths. 



" A careful examination of the surfaces showed that the uniformity of 

 the indentations from impinging was constant, and the conclusion was, that 

 the new forms assumed were in no wise affected by any inequality of this 

 action. 



" On breaking the specimens, the internal structure of each ball was 

 nearly the same, exhibiting an effort to form prismatic crystals radiating from 

 a centre on one side of the void, while every particle seemed to have changed 

 its place and made a new aggregation. Where before the texture was small- 

 granular, broad and brilliant-bladed crystals were found, with open inter- 

 stices, while in the space originally void the terminal points of many crystals 

 made it a geode in appearance. 



"In offering an explanation of this extensive change among the mole- 



