92 DUDLEY. 



Pront truck rear tender wheels, 3^20 



Center of space between tender trucks, 1530 



Front wheel rear tender truck, 6100 



Center of space between wheels, 0000 



Rear wheel of rear tender truck, 6870 



The shaded ballast under the ties in Plate X., Fig. 2 is an ideal 

 representation of the distribution of the pressure of the wheel 

 loads through the rails, ties and ballast to the road-bed, the 

 darker portions representing the most intense pressures. Under 

 moving trains the wheel loads are transmitted as a series of 

 weaves of pressure to the ballast and road-bed. 



A series of alternating stresses run through the rails in con- 

 sonance with the speed of the trains, the waves of greatest in- 

 tensity being between the ties. Some of the slides will show 

 that the tremors and vibrations of the rails are very decided 

 under the wheels passing in quick succession. The duration 

 of the greatest intensity of the stress of the metal is very short 

 per lineal inch, being only a fraction of a second for the high 

 speed trains, less than 1/250 of a second for a speed of 40 miles 

 per hour ; while the maximum stress increases with the speed, 

 the duration of greatest intensity decreases. 



A rail in the track, like any other girder, to carry its loads 

 without taking a permanent set, must not have the metal 

 stressed beyond its elastic limits and it should be much less for 

 a proper factor of safety. 



The diagrams of the earlier steel rails, which I have previ- 

 ously shown, indicate that nearly all the rails had taken more 

 or less permanent set ; therefore, the fiber stresses in the rails at 

 times had exceeded the elastic limits. 



This important fact must be borne in mind, for the stresses 

 Avhich occurred in the early steel rails, even for the lighter 

 equipment, were greater than I shall report for the present 

 80-lb. rails. The stresses in rails may be much greater than 

 would be permissible in bridge members, for in the latter they 

 are of several seconds' duration and the material a much lower 

 grade of steel. High stresses in rails are not of recent origin, 

 but occurred a few times daily in the early rails. The rails 



