AUTOGRAPHIC DIAGRAMS. 



239 



showing that when the limit has been passed there is 

 a rapid yielding of the substance with a diminution of 

 load. 



On Fig. 112 will be seen two diagrams taken with Mr. 

 Wicksteed's autographic apparatus. That marked A is 

 from a specimen of mild steel, while B is taken from a 

 tension specimen of copper. The general form of these 

 curves is similar to those taken by Professor Kennedy's 

 instrument, and it will be noticed that the turning back of 

 the curve just beyond the limit is again well marked. 

 In this apparatus, as the load ordinate is proportional to the 



120 



ISO 



360 



is>J80 



210 



300 



240 



270 



FIG. 117. Torsion Diagram for Mild Steel Specimen. 



actual load on the specimen, and is independent of the 

 movement of the poise, the portion of the diagram repre- 

 senting the last stage of the test during which the local 

 extension takes place is automatically produced. 



The diagrams of Figs. 113 and 114 are samples of the 

 curves produced by the Richie" apparatus. Of these, Fig. 113 

 is for a mild steel tension test; Fig. 114, C, is from a 



