96 DUDLEY. 



largest stress was only 13,500 lbs. on a 4^<-inch rail for a load 

 of 16,000 lbs. on drivers. 



Mr. Howard in 1893, 4 and 5 repeated the tests on other rail- 

 road tracks and heavier rails and found apparently higher stresses. 

 I repeated the experiments on rails in the tracks, and the results 

 seeming low I had solid piers erected and with rails 30 feet long 

 under known stresses I found my results were too low. 



With micrometers designed for the work the results for static 

 loads should be fairly accurate. 



The determination of the stresses or rather the compression 

 and elongation of the metal in the base of the rail under moving 

 trains is a much more difficult problem, or rather a series of 

 problems, than it is for static loads, and I am not aware that 

 any one has attempted their solution before I attacked them 

 the past year with my Stremmatograph and its accessories. 



A mathematical expression for the stresses of rails under 

 moving trains, its span for the ties and wheel spacing, the deflec- 

 tion and compression of the ties, ballast and road-bed, has not 

 been fully determined, though many efforts to do so have been 

 made. 



Such a formula would also have to consider the many condi- 

 tions of the path not only described by the centre of gravity of 

 the locomotive, tender and each car of the train, but also those 

 of the rotating wheels, their mass and speed, the smoothness of 

 the rails and the more or less sudden application of the loads. 



The principle of the Stremmatograph is to record on a mov- 

 ing metallic strip the molecular compression or elongation of 

 the metal in a given length of the base of the rail, induced by 

 the stresses, produced by each wheel of the moving trains under 

 the many conditions of service. 



These records can be measured by filar micrometers under a 

 microscope and then from the modulus of elasticity of the steel 

 compute the stresses which produce the given compression or 

 elongation per square inch of the extreme fibres in the base of 

 the rail. [See Plate X, Fig. 3.] 



The object of the Stremmatograph is to convert rails of any 

 section and weight, of any system of permanent way construe- 



