in the Internal Structure of Iron, 291 



force of every blow produced by the numerous causes incidental to rail- 

 way transit ; by causing the whole weight of the entire body in motion, 

 fo act by its momentum in consequence of the perfect rigidity of the 

 several parts and the manner of their connection with each other, instead 

 of such a degree of elasticity as would render the different parts nearly 

 independent of one another, in the case of sudden jerks or blows ; and 

 which rigidity must produce very great mischief both to the road and to 

 the machinery moving upon it. The looseness of the axles in their brasses 

 must also be another cause which would greatly increase this evil. 



Although I have more particularly alluded to the change in the inter- 

 nal structure of iron with reference to the effects on railway- axles, it need 

 scarcely be observed that the same remarks would apply to a vast number 

 of other eases, where iron, from being more or less exposed to similar 

 causes of action, must be similarly acted upon. The case of railway-axles 

 appears to be of peculiar and pressing importance, well deserving tlic 

 most serious consideration of scientific men, and particularly deserving 

 the attention of those connected with railways, or othervvays engaged in 

 the manufacture of railway-machinery, who have the means of testing the 

 accuracy of the theory here proposed. For if the views I have stated be 

 found to harmonize with the deductions of science, and to coincide with 

 the results of experience, they may have a very important effect upon 

 public safety. It may be observed, on the other hand, however, that at 

 the present time all railway-axles are made infinitely stronger than would 

 be necessary for resisting any force they would have to sustain in pro- 

 ducing fracture, provided the iron were of the best quality ; and to this 

 circumstance may perhaps be attributed the comparative freedom from 

 serious accidents by broken axles. The necessity for resisting flexure 

 and the effects of torsion, are reasons why railway-axles never can be 

 made of such dimensions only as would resist simple fracture ; but it 

 would be very desirable to possess some accurate experiments on the 

 strength of wrought iron in different stages of its crystallization, as there 

 can be no doubt that very great differences exist in this respect, and it is 

 probable that in most cases, when the crystallization has once commenced, 

 the continuance of the same causes which first produced it goes on con- 

 tinually increasing it, and thereby further reduces the cohesive strength 

 of the iron. 



E.vuL Street, May 31. 1842. 

 [Several samples of broken railway-axles accompanied this paper, and 

 were exhibited at the meeting. In some of them the same axle was 

 broken in different places, and shewed that where the greatest amount of 

 percussion had been received, the crystallization of the iron was far more 

 extensive than in those parts where the percussion had been less.] 



