AUTOGRAPHIC DIAGRAMS. 



have already been described to which autographic devices 

 are attached. The Buckton torsion machine draws a spiral 

 diagram on a disc, which is rotated by connection with 

 the free end of the specimen, and which is made to 

 revolve through the same angle. The radial movement of 

 the pencil in this apparatus is derived from the movement 

 of the poise weight, which is used to increase the twisting 

 moment on the specimen. The autographic apparatus 

 attached to the Deely torsion machine has already been 

 mentioned. This is really a Crosby steam-engine indicator,, 



8O 



100, 



20 .40 60 



Loads in thousands of pounds. 



C Cold rolled steel. 



D Muntz metal. Specimens, 1 in. long and in. diameter. 



FIG. 114. Autographic Compression Diagrams, from Richie's 

 Apparatus. 



the rotatory movement of the drum being derived from the- 

 twist of the specimen, and the pencil movement depending 

 upon the motion of the lever against the controlling spring. 



131. Autographic Diagrams. The diagrams produced 

 by these various appliances are of course similar in form to 

 diagrams plotted from sets of recorded observations, and 

 should be, putting aside defects and inaccuracies of the 

 apparatus used, precisely the same. Examples of diagrams- 

 produced by the appliances just mentioned will be seen on 

 the following figures. 



On Fig. ill are shown three samples of diagrams taken 

 with Professor Kennedy's apparatus. In this case the load 

 abscissae lie on parallel circles, although the stretch 

 ordinates are in vertical straight lines. In order to com- 

 pare diagrams of this kind with those having rectangular 



