DEELEY TORSION MACHINE. 205 



to the boss of a lever L. The test-bar is marked A. 

 The specimens used are comparatively short ones. 

 The great difference between this and the other torsion 

 machines is in the arrangement of the measuring lever. 

 Here, instead of having the lever resting on the knife edge, 

 as is the usual practice, the hollow centre, which holds one 

 end of the test bar and forms part of the lever, is held in 



Position by what is in effect an elastic frictionless support, 

 his consists of the three steel plates marked K on the 

 side elevation above, attached to three corners of a triangular 

 frame which is bolted to the bed plate. By holding the 

 centre in this way, the lever is allowed to rotate through a 

 very small angle, and be at the same time supported in 

 position. The centre, which carries the other end of the 

 test piece, instead of being rigidly attached to the worm 

 wheel, is connected with it through three links, which are 

 attached to the ends of a three-armed lever forming part of 

 the centre, being rigidly keyed to it. This arrangement 

 allows the necessary end play of the specimen. 



The manner of measuring the twisting moment is 

 rather unusual. Instead of having a moving jockey- 

 weight, and estimating the moment as the product of 

 this weight into its distance from its zero position, the 

 moment is measured at a constant arm, and by means 

 of a spring, as in a steam-engine indicator. This will be 

 clearly seen in the illustration. The end of the lever 

 presses upon a vertical rod which is attached to the lower 

 end of a spring of known strength, and as the twist is put 

 upon the test bar by means of the worm wheel, the outer 

 end of the lever is pressed downwards and the spring is 

 slightly extended, the actual amount of the strain 

 being proportional to the downward force exerted by 

 the lever end. The extent of the strain of the spring, and 

 therefore of the twisting moment also, is indicated by the 

 movement of a rotating pointer on the dial shown. The 

 gauge is directly graduated by attaching a balanced lever 

 to the elastic centre, and loading it to the moments 

 required. The indications given are marked upon the dial, 

 which is graduated so as to give the load in tons acting 

 at an arm equal to the radius of the test bar used, 0'399 of 

 an inch. This value can be reduced to any other terms as 

 may be wished. The standard size of test bar used in this 

 machine is shown on Fig. 99, the diameter being arranged 

 to give a cross section of one-half a square inch. 



An autographic diagram may be drawn by means of the 



