588 Proceedings of the British Association, 



and the Paris and Versailles railways, would show that they arose 

 from other causes, and had no reference to the engine having four 

 wheels or six. He considered that both accidents arose from similar 

 causes : in both cases heavy trains and two engines where coupled 

 together, the smaller one leading ; from some cause a check took place, 

 the engine-man shut off the steam of the leading engine, and the 

 following engine, with the immense momentum derived from weight 

 and velocity, struck against it, forcing it off the rails, and causing 

 the overturn of the carriages. Tt was considered objectionable to 

 use an auxiliary engine behind a train, because, in case of any retard- 

 ation of the engine in front, it cannot be checked in time to prevent 

 great concussions of the carriages. Similar objections applied to using 

 two engines under any circumstances, especially when of unequal 

 power. Many accidents had taken place in consequence of the break- 

 ing of cranked axles ; and M. Francois and Col. Aubert, in their report 

 to the French government, had remarked that the fractures of broken 

 axles, instead of the fibrous appearance of wrought iron, presented the 

 crystallized appearance of cast iron, which they attributed to magnetic 

 or electric changes in the molecular structure of the iron, caused by 

 friction in the bearings and great velocities ; "and in his opinion it was 

 probable that the continual strains and percussions to which the crank 

 axle is subjected will account for the changes in the molecular constitu- 

 tion of the iron. 



Mr. Hodgkinson was certain, from the results of his experiments, 

 that a succession of strains, however slight, would produce a permanent 

 deterioration of the elasticity of the iron — Mr. Fairbairn had been 

 told by the engineer on the Leeds line, that he considered all crank 

 axles to be constantly deteriorating from percussions, strains, &c , and 

 that they should be removed and replaced by new ones periodically, to 

 avoid danger of fracture. — A discussion arose as to whether the crys- 

 tallized appearance observed in fractured axles arose from defects 

 in the manufacture, in the quality of the iron, or from the effects 

 of working, either by percussions, strains, or magnetic action. — Mr. 

 Grantham, although a manufacturer of cranked axles, admitted that 

 straight axles were less liable to break. Cranked axles, from the 

 way in which they were welded together and shaped, were rendered 

 weak and liable to fracture. On other grounds, however, he believed 

 that the cranked axles were preferable, as they produced a steadier 

 motion, and much heat was saved. — Mr. Garnett believed that more 

 straight axles had broken than cranked ones. — Prof. Willis showed 

 the effect of vibration in destroying molecular arrangement, by refer- 



