STREMMA TOGRAPH. 105 



The results show some of the phenomena displayed by rails 

 in service under static conditions of loading or when a loco- 

 motive passes slowly over the track. 



The tests will in a measure supplement laboratory experi- 

 ments in this class of material, in addition to the aid which they 

 may afford to practical questions pertaining to maintenance of 

 way. 



The series were made chiefly on the track of the Pennsylvania 

 Railroad, where exceptional opportunities existed for examining 

 road-bed, embracing a wide variety of conditions of weight of 

 rails and different kinds of ballast, and its behavior under heavy 

 types of freight and passenger locomotives. 



The tests were made during the early part of the month of 

 November, 1894, on track in the condition it was found in ser- 

 vice. 



The experiments on the Boston & Albany Railroad were 

 made, with track on frozen gravel ballast, in the month of 

 February, 1895. 



Describing the methods of making the experiments, the fibre 

 stress tests were made by means of a micrometer mounted on 

 the upper side of the outer flange of the base of the rail, at a 

 place midway adjacent ties. The instrument covered a gauged 

 length of 5 inches. 



The micrometer was adjusted in position, and then the several 

 wheels of the locomotive were successively brought over the 

 gauged length, or until the same was midway adjacent wheels. 



The instrument was read when the locomotive was at each of 

 these positions. It was found practicable to make the microm- 

 etre observations without arresting the locomotives in all 

 cases, taking the readings as the locomotives passed slowly over 

 the rail. 



In this manner the strains developed were measured, and 

 elongation of the metal showing tensile stress, and a contraction 

 in the gauged length showing compressive stress. 



The measured strains were reduced to stresses per square 

 inch, assuming the modulus of elasticity of the steel to be 30,- 

 000,000 lbs. per square inch, and correcting the observed strain 



