RAILWAY CONSTRUCTION. 217 



although an extra thickness was given to that part of the 

 section. The cast-iron was exposed to the greatest strain at 

 the point where it was the least capable of offering resistance. 



Much ingenuity was displayed in many of the patterns 

 brought forward, but in dealing with a hard unyielding material 

 like cast-iron, it is difficult, if not impossible, to impart any soft, 

 elastic effect; and the different systems of cast-iron sleepers 

 failed to become popular on our home railways, on account of 

 the noise and vibration when trains passed over them. Another 

 objection was the great multiplicity of parts required in many 

 of the types, and the constant and severe strain produced on the 

 fastenings on the passing of every wheel. The bolts might be 

 made tight at first, but the incessant shaking would work them 

 loose, the threads became stripped, and the rails ceased to be 

 held in a proper and secure position. 



The cast-iron sleeper road was considered unsuitable for the 

 heavy and fast traffic of our home lines, and was ultimately all 

 taken up and replaced with wooden transverse sleepers. At the 

 same time, there is no doubt that cast-iron sleepers have been of 

 great value in India and tropical climates, where timber sleepers 

 were not only scarce, but perish very rapidly. Very large 

 numbers of them have been laid down abroad of patterns very 

 similar to those shown in Figs. 309, 310, and 311, and have done 

 good service for many years. They are not affected by rain or 

 heat, but, unfortunately, being castings y are liable to considerable 

 annual loss from breakage. 



Improvements in plate-rolling machinery, and in appliances 

 for bending and stamping wrought-iron, have materially assisted 

 in developing the introduction of wrought-iron and steel sleepers. 

 Cast-iron and wrought-iron are, in the abstract, hard and non- 

 elastic as compared with wood ; but whereas cast-iron can only 

 be made into fixed, unyielding shapes, wrought-iron and steel 

 can be worked into forms that possess a certain spring-like 

 effect, which not only enables them almost entirely to resist 

 fracture, but also imparts a measure of elasticity to the per- 

 manent way. 



The simplest form of wrought-iron sleeper would be a plain, 

 flat plate, to which the chair, or rail-bracket, would be attached ; 

 but as this form would have bearing surface only, without any 

 lateral hold on the ballast to keep the rails to line, it could not 

 be adopted. 



