in the Internal Structure of Iron. 289 



stances ; but the necessary force of vibration among Its particles only ex- 

 tended for a short distance, and to that extent only did the crj-stallization 

 proceed. The effect of magnetism in assisting the crystallization, I think it 

 unnecessary to dwell upon, as the extensive use of galvanic currents in 

 modern times has fully proved their power in crystallizing some of the 

 most refractory substances; but by themselves they are unable to produce 

 these effects on iron^ or at least the operation must be extrcmel}* slow. 



Another circumstance which occurred under Mr Manby's observation, 

 confirms generally the preceding opinions. A small bar of good tough 

 iron was suspended and struck continuously with small hand-hammers, 

 to keep up a constant vibration. The bar, after the experiment had been 

 continued for some considerable time, became so extremely brittle, that 

 it entirely fell to pieces under the light blows of the hand-hammers, pre- 

 senting throughout its structure a highly crystallized appearance. 



The fracture of the axles of road-vehicles of all kinds is another in- 

 stance of the same kind. I have at different times examined many 

 broken axles of common road-vehicles, and I never met with one 

 which did not present a crystallized fracture ; while it is almost cer- 

 tain that this could not have been the original character of the iron, 

 as they have frequently been used for years with much heavier loads, 

 and at last have broken without any apparent cause, with lighter 

 burdens and less strain than they have formerly borne. The ef- 

 fects, however, on the axles of road-vehicles are generally extremely 

 slow, arising, I apprehend, from the fact that, although they receive a 

 great amount of vibration, they possess a very small amount of magnet- 

 ism, and are not subject to a high temperature. The degree of magnet- 

 ism they receive must be extremely small, from their position and con- 

 stant change with regard to the magnetic meridian, the absence of 

 rotation, and their insulation by the wood-spokes of the wheels. Whether 

 the effects are equally slow with iron-wheels used on common roads, may 

 perhaps admit of some question. With railway-axles, however, the case 

 is very different. In ever}' instance of a fractured railway-axle, the iron 

 has presented the same crystallized appearance j but this effect, I think, 

 we shall find is likely to be produced far more rapidly than we might at 

 first expect, as these axles are subject to other influences, which, if the 

 theory here stated be correct, must greatly diminish the time required to 

 produce the change in some other cases. Unlike other axles, those used 

 on railways rotate with the wheels, and consequently must become, dur- 

 ing rotation, highly magnetic. Messrs Barlow and Christie were the 

 first to demonstrate the magnetism by rotation produced in iron, which 

 was afterwards extended by Messrs Herschel and Babbage to other 

 metals generally, in verifying some experiments by M. Arago. It can- 

 not, I think, 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 



