STREMMATOGRAPH. 93 



would stand some millions of repetitions of stress nearly up to the 

 elastic limits before fracture would occur. If such stresses are 

 of a half hour or longer intervals some recovery in the metal 

 takes place ; but when fracture does commence, it seems to start 

 between individual adjacent mineral aggregates, rather than 

 through them, becomes progressive, and in many cases the 

 complete rupture of the section may take one or more years of 

 further service. 



The tests of many of the earlier steel rails show that the 

 elastic Hmits only ranged from 35,000 to 48,000 lbs., the ulti- 

 mate strength being about twice those amounts respectively. 



In the testing machine it takes 30,000 pounds tension to 

 elongate one square inch of steel per lineal inch i/iooo of an inch 

 and the same force to compress it, which was nearly all the 

 early steel rails permitted the extreme fibres in the base of the 

 rail to be extended or compressed before set would occur. 

 This margin was too small, and as the traffic increased it was 

 impossible to maintain the tracks to a high standard even at a 

 very large cost for labor. These facts lead me to urge the 

 adoption of stiffer and heavier rails with higher elastic limits 

 which would reduce the fibre stresses much below the elastic 

 limits of the steel, increase the factors of safety and not require 

 so much labor to maintain them to a high standard in the 

 track. 



When I look over the diagrams of the earlier steel rails, it is 

 difficult to realize that it is only fifteen years since I designed 

 the pioneer 5 -inch 8o-lb. steel rail for U. S., which was rolled 

 for and put into service in 1884, by the N. Y. C. & H. R. R.R. 



The Pennsylvania Railroad and others soon followed with 

 5 -inch sections of 80 or 85 lb. ; 80 lbs. becoming very general 

 on Eastern Trunk Lines, forming a distinct epoch in the devel- 

 opment of American Railways. 



It takes many years to change the section of rails on a long 

 main line, while the design of new equipment and construction 

 is but a few months' work and easily keeps in advance of the 

 permanent way improvements. 



The slide on the screen is from a photograph of the " Empire 



