548 RAIL-ROADS. 



laid on cross sleepers even with the ground. In process 

 of time the rails were found more convenient, at a small 

 elevation, clear from dirt and other accidental obstruc- 

 tions ; and the renewing the rails when worn down, be- 

 coming inconvenient, the contrivance of a scantling or 

 upper rail was adopted, and this being pinned upon the 

 principal strong piece could be easily replaced. At this 

 period wooden wheels were used, and the load conveyed 

 was about two and a half times that on the ordinary roads. 

 The inclination of the rail was graduated merely for this 

 draft, which appeared to satisfy all the expectations of the 

 period. After many years thin iron plates were placed 

 upon the wooden scantling, wherever the friction became 

 great from turnings or acclivities. Rail-roads continued 

 much in this state until about 1776, when cast iron rails 

 were introduced in the shape of the ' plate rail,' or tram 

 rail-road, having the flange or rim upon the rail. All 

 rails requiring the flange to be upon the wheel are called 

 ' edge rails.' Cast iron wheels were first used with the 

 iron rails, and it is only about thirty years since that stone 

 supports became common instead of the wooden sleepers. 



In 1790 the edge rail was invented, and this is now 

 most approved. Square bars of wrought iron were tried 

 about tvventyfive years since with success ; and iron roll- 

 ed nearly into the form of the edge rail was also in use 

 about ten years since. 



From some extensive experiments made in England on 

 the comparative strength of cast and wrought iron, the 

 results were in favor of the latter. The greater vibration, 

 however, is a serious objection. 



The cast iron rails of certain length nveighing fifty- 

 seven pounds per yard required seven and a half tons to 

 break them. 



The wrought iron rails of same length weighing twen- 

 tyeight pounds per yard required six and a half tons to 

 overcome their permanent elasticity, and in this case 

 there was a deflection or bend of one tenth of an inch in 

 four feet. These rails were made for four tons on wheels, 

 and it appears that the absolute strength of the rail should 

 exceed the ordinary strain or load at least as three to one. 

 The strongest wrought iron rails required are thirty five 



