subsequent to its Manufacture. 13$ 



be doubted, that all railway axles become from this cause 

 highly magnetic during the time they are in motion, though 

 they may not retain the magnetism permanently. But in the 

 axles of locomotive engines we have yet another cause which 

 may tend to increase the effect. The vaporization of water 

 and the effluence of steam have already been stated to produce 

 large quantities of negative electricity in the bodies in con- 

 tact with the vapour; and Dr. Ure has shown* that negative 

 electricity, in all ordinary cases of crystallization, instantly 

 determines the crystalline arrangement. This of course must 

 affect a body of iron in a different degree to that of ordinary 

 cases of crystallization ; but still we see that the effects of 

 these various causes all tend in one direction, producing a 

 more rapid change in the internal structure of the iron of the 

 axle of a locomotive engine, than occurs in almost any other 

 case. 



Dr. Wollaston first pointed out that the forms in which 

 native iron is disposed to break, are those of the regular oc- 

 tahedron and tetrahedron, or rhomboid, consisting of these 

 forms combined. The tough and fibrous character of wrought 

 iron is entirely produced by art ; and we see in these changes 

 that have been described, an effort at returning to the natural 

 and primal form ; the crystalline structure, in fact, being the 

 natural state of a large number of the metals ; and Sir Hum- 

 phry Davy has shown that all those which are fusible by or- 

 dinary means assume the form of regular crystals by slow 

 cooling. 



The general conclusion to which these remarks lead us, 

 appears, I think, to leave no doubt that there is a constant 

 tendency in wrought-iron, under certain circumstances, to re- 

 turn to the crystallized state; but that this crystallization is 

 not necessarily dependent upon time for its development, but 

 is determined solely by other circumstances, of which the 

 principal is undoubtedly vibration. Heat, within certain li- 

 mits, though greatly assisting the rapidity of the change, is 

 certainly not essential to it; but magnetism, induced either 

 by percussion or otherwise, is an essential accompaniment of 

 the phenomena attending the change. 



At a recent sitting of the Academy of Sciences at Paris, 

 M. Bosquillon made some remarks relative to the causes of 

 the breaking of the axle on the Versailles Railroad ; and he 

 appears to consider that this crystallization was the joint ef- 

 fect of time and vibration, or rather, that this change only 

 occurs after a certain period of time. From what has here 

 been said, it will be apparent that a fixed duration of time is 



* Journal of Science, vol. v. p. 106. 



