189I.] NEW-YORK MICROSCOPICAL SOCIETY. 117 



of the texture, and at the same time keep the phosphorus down to 

 avoid brittleness. 



In 1883 I designed an 8o-pound section, which makes the struc- 

 ture of the metal in the head much finerthan usual. The section 

 was put into service in 1884, the manufacture of which became 

 the type of modern sections. Over 200,000 tons of this section 

 have been put into service, some of the rails having .50 in car- 

 bon. Even with so much carbon the elastic limits of the steel 

 are below what is necessary for modern traffic, and I am now mak- 

 ing rails with .60 carbon, the phosphorus being down to or under 

 .06. Specimen No. 4 shows a piece of steel from such a com- 

 position which is very fine-grained for a large rail, tough, and 

 has a tensile strength of 120,000 to 130,000 in the head, the elas- 

 tic limits ranging from 60,000 to 65,000 pounds. Such rails can 

 be produced commercially, the cost only being increased about 

 one-tenth above the cost of ordinary rails. 



Without microscopic examination it is difficult to see why it is 

 so important to make the rails of fine texture and high elastic 

 limits. If a rail simply had to perform the functions of a girder, 

 we could increase its dimensions so that it would have ample 

 strength, even though the elastic limits of the metal were low. 

 But the upper surface of the rail must also act as the infinitesi- 

 mal rack by which the drivers secure their adhesion for locomo- 

 tion. Tracing these matters out more fully, we find the metal, 

 in the head of the rail under a driver, in compressionto the vertical 

 axis of the section, while the metal under the neutral axis would 

 be in extension, which would reach to each tie, beyond which, as 

 far as affected by the weight of that driver, the base would be in 

 compression and the head in extension. These strains would 

 be reversed as the driver or wheel reached the next tie space. 

 The metal in the head directly under the wheel must not only 

 bear the weight upon the driver, but also all the traction the 

 driver is exerting to draw the train. From the small areas in 

 contact, the ratio of pressure is from 60,000 to 80,000 pounds per 

 square inch, while the traction often amounts to one-half as much 

 for the surfaces in contact as longitudinal strain upon a thin 

 layer of surface metal in the rail head. Examining the rails in 

 the track with the microscope, we find not only small portions of 

 the metal torn out, but a series of minute cracks, showing that 



