TRANSACTIONS OP THE SECTIONS. 105 



dent had ever occurred from breakage ; and such increase of room had been ob- 

 tained, that they had placed the tender underneath the engine, thus fixing the centre 

 of gravity as low as possible, and dispensing with the separate tender. By this 

 arrangement they could run fifteen miles without stopping for water. He had found 

 much difficulty in introducing the straight-axled engine on this line ; and, in fact, 

 the great obstacle in obtaining a fair trial for different forms of engines arose from 

 the fluctuation in public opinion. Straight axles and cranked axles, four-wheeled 

 and six-wheeled engines, had been used on different lines, not so much from the 

 recommendations of the engineer as in compliance with the opinion of the several 

 railway boards. Just now a prejudice existed against four-wheeled engines, as being 

 less safe than six-wheeled, more liable to run off the line, &c, whereas he con- 

 tended that the four-wheeled engine per se was not open to these objections. He 

 believed that the principal advantage which could be claimed for the six-wheeled 

 engine was in the disposition of the weight on the wheels, and having the third pair 

 of wheels and axle, in case of accident to either of the other pair ; and a consideration 

 of the fatal accidents which had lately occurred on the London and Brighton 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 

 were 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. It was 

 considered objectionable to use an auxiliary engine behind a train, because, in case 

 of any retardation 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 breaking of cranked axles ; and M. Francois and 

 Col. Aubert, in their report to the French government, had remarked that the frac- 

 tures 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 cranked axle is subjected will account for the changes in 

 the molecular constitution of the iron. 



On the Strength of hammered and annealed Bars of Iron and Railway 

 Axles. By James Nasmyth. 



In locomotive engines the axle was the chief point of danger ; and it was there- 

 fore important, both as a scientific and practical question, to determine the nature 

 and habitude of iron when placed under the circumstances of a locomotive axle. 

 Experiment was the only way to discover this, and he would have wished to place 

 iron under exactly similar circumstances ; but the short time intervening since 

 the subject had come before the Section had rendered it impossible to do so. One 

 opinion was, that the alternate strains in opposite directions, which the axles were 

 exposed to, rendered the iron brittle, from the sliding of the particles over each other. 

 To illustrate this, Mr. Nasmyth took a piece of iron wire and bent it back and for- 

 ward ; it broke in six bends. He had suggested annealing as a remedy for this de- 

 fect : in proof whereof he took a piece of annealed wire, which bore eighteen bends, 

 showing an improvement of three to one in favour of annealing. He should there- 

 fore advise railway companies to include in their specification, that axles should be 

 annealed ; and would moreover most strongly recommend that where any doubt 

 existed as to a change for the worse having (from whatsoever cause) taken place in 

 respect to deterioration of the tenacity of the iron of the axle, the simple but effective 

 process of annealing should be had recourse to, which would be found to restore its 

 original toughness ; he did not like the custom of oppressing engineers with useless 

 minutiae in specifications, but this was so useful and so cheap, that he thought it 

 ought to be insisted on. To exhibit on a larger scale the effect produced on iron in 

 our workshops, he showed a specimen of iron as it came from the merchant : 

 being nicked with a chisel, it broke in four blows with a sledge, at the temperature 



