subsequent to its Manufacture. 133 



ceives is to produce magnetic induction, and that magnetic 

 induction and consequent polarity of its particles, when as- 

 sisted by further vibrations from additional percussion, pro- 

 duces a crystallized texture. For it is perfectly well known 

 that in soft iron magnetism can be almost instantaneously pro- 

 duced by percussion ; and it is probable that the higher the 

 temperature of the bar at the time it receives the magnetism, 

 the more likely will it be to allow of that re-arrangement of 

 its molecules which would constitute the crystallization of the 

 iron. 



It is not difficult to produce the same effects by repeated 

 blows from a hand-hammer on small bars of iron ; but it ap- 

 pears to depend upon something peculiar in the blow, which 

 to produce the effect must occasion a complete vibration 

 among the particles in the neighbourhood of the part which 

 is struck. And it is remarkable that the effects of the blows 

 in all cases seem to be confined within certain limited di- 

 stances of the spot which receives the strokes. Mr. Charles 

 Manby has mentioned to me a circumstance which fully bears 

 out this statement. In the machine used for blowing air at 

 the Beaufort Iron Works, the piston-rod of the blowing cy- 

 linder, for a considerable time, had a very disagreeable jar in 

 its motion, the cause of which could not be discovered. At 

 last the piston-rod broke off quite short, and close to the 

 piston ; and it was then discovered that the key had not pro- 

 perly fastened the piston and the rod together. The rod at 

 the fracture presented a very crystallized texture ; and as it 

 was known to have been made from the very best iron, it ex- 

 cited considerable surprise. The rod was then cut at a short 

 distance from the fracture, and it was found to be tough and 

 fibrous in a very high degree ; showing what I have already 

 pointed out, that the effects of percussion generally extend 

 only a very short distance. In fact, we might naturally ex- 

 pect, that as the effect of vibration diminishes in proportion 

 to the distance from the stroke which produces it, so the cry- 

 stallization, if produced by this means, would also diminish 

 in the same proportion. The effect of magnetism alone may 

 also be estimated from this circumstance. The rod would of 

 course be magnetic throughout its whole length ; this being 

 a necessary consequence of its position, independent of other 

 circumstances; but the necessary force of vibration among 

 its particles only extended for a short distance, and to that 

 extent only did the crystallization proceed. The effect of 

 magnetism in assisting the crystallization, I think it unneces- 

 sary to dwell upon, as the extensive use of galvanic currents 

 in modern times has fully proved their power in crystallizing 



