90 DUDLEY. 



base of the locomotives and cars, the greatest deflection being 

 directly under the wheels. 



To carry and distribute the wheel loads to the ties, ballast 

 and road-bed, the rail acts as a girder, the metal in the rails 

 directly under the wheels above the neutral surface is in com- 

 pression, while that below the neutral surface is in tension. 



On and near the supporting ties, shearing stresses are set up 

 extending through the web of the rails as the w^heels pass over 

 the rails. 



The span of the deflection of the rails under the wheels is 

 longer as a rule than the tie spacing, and in a short distance on 

 either side of the wheels the nature of the stresses is reversed, 

 the head of the rails being in tension and the base being in com- 

 pression. 



The picture on the screen is a representation of the wheel 

 loads and base of a Boston and Albany lOO-ton locomotive 

 standing on 9 5 -lb. rails, showing in figures the actual depression 

 of the rails, ties and road-bed under the static loads. The rails 

 under moving trains rise slightly in front of the pilot. [See 

 Plate X., Fig. 2.] 



The dotted line directly over the rail indicates its general de- 

 pression under the wheel loads and base of the locomotive. 



The vertical scale is enlarged to render the depressions more 

 distinct ; the greatest deflections in the rails and road-bed being 

 directly under the wheel contacts. 



The truck wheels carry 20,350 lbs. per. pair ; the drivers 

 37,500 lbs. per pair; the front tender wheels 18,500 lbs. per 

 pair, and the rear ones 23,500 lbs. per pair. The depression 

 and deflection shown for one rail is, therefore, for wheel loads 

 only one-half of that per pair of wheels. Locomotives with 

 much greater weights on the drivers are in general use. 



The depression under the front truck wheel of the engine was 

 0.094 of an inch ; between the wheels 0.086 of an inch, and 

 under the rear truck wheel o. 100 of an inch. 



In the wheel space between the engine truck and front drivers 

 the depression was 0.088 of an inch ; under the front driver 

 0.138 of an inch ; in the wheel space between drivers 0.096 of 



