438 



EEPOKT — 1891. 



The form of the diagram for a piece of mild steel is shown 

 in the woodcut, from which it will be seen that the extension 

 produced by a given load is represented as an abscissa, while 

 the load itself is represented as a curved ordinate. The 

 diagram represents the behaviour of the specimen during the 

 test, and shows clearly the limit of elasticity, the maximum 

 load, and the elongation. The curve not only indicates the 



Diagrams taken with Professor Kenneclifs Apparatus. 



EXT ENSUON 



No. 1. Lanclore Eivet-steel : Yicld-poiut, 17-39 tons per sq. in. j\Iax. 

 load = 27-29 tons. 



No. 2. Swedish Bar-iron : Yield-point, 12-G7 tons per sq-. in. Max. 

 load = 18-85 tons. 



yield-point, and the amount of extension which occurs at this 

 point, but it is seen by inspection that the local extension 

 which occurs at the breaking-point is measured by drawing 

 ordinates at the connnencement and termination of the curve 

 drawn during the time the specimen is undergoing local exten- 

 sion. Again, the area of the diagram represents the gross 

 mechanical value of the material, as it represents the work 

 done in breaking the bar, which of course depends upon its 

 breaking-strength and ductility. 



The principle of the apparatus is as follows : The test- 

 piece is placed in the machine with a stronger bar, which is 

 called a spring-piece. The material of this bar must be ascer- 

 tained by previous experiments to be perfectly elastic, so that 

 its extensions are strictly proportional to the pull on the test- 

 piece ; and, moreover, it should be of such an area that its limit 

 of elasticity occurs only at a load greater than that which will 

 break the test-piece. By a simple arrangement a very light 

 pointer is made to swing about an axis through an angle pro- 



