TORSIONAL TESTING MACHINES. 



199 



(6) If the beam is initially floating horizontally, as the 

 jockey-weight is moved outwards, the twisting moment on 

 the bar is increased. The bar consequently twists or takes 

 a torsional strain and the beam sinks from its horizontal 

 position. The end of the bar remote from the beam must 

 be held so as to be rotated at the will of the operator. 

 This is generally accomplished by having the end of the 

 bar fixed in the axis of a worm wheel, which can be rotated 

 either by hand or power. The centre of the worm wheel 

 is bored out so as to receive the end of the bar, which is 

 prevented from rotating by keys. 



In individual machines the details are varied somewhat 

 but the general arrangement is the same in nearly all cases. 



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r 



7 



FIG. 93. Kennedy's Original Torsion Machine. 



1 10. Professor Kennedy's Torsional Testing Machine. 



On Fig. 93 is represented in plan the arrangement 

 adopted in Professor Kennedy's original torsional testing 

 machine, and which forms the basis of most modern 

 torsion machines. The view is diagrammatic. The speci- 

 men is marked S, and consists of a circular bar of the 

 material to be tested, with turned ends. The end nearest 

 the top of the page is made to fit easily into the boss of 

 the worm-wheel marked A. The other end fits in a 

 similar way into the boss of the steelyard B, the axis of 

 the hole into which it fits coinciding with the line of the 

 knife-edge about which the steelyard rotates. In order 



