210 



MEASUREMENT OF TORSIONAL STRAINS. 



same nominal strength. The errors caused by the deforma- 

 tion of the machine were found to be extremely small. The 

 machine used in these tests was one of Mr. Wicksteed's 

 small torsion machines similar to that shown in Fig. 94. 

 Here the handwheel used for rotating the worm was 

 divided into 24 equal arcs, each equivalent to 10 

 minutes, as the worm wheel had 90 teeth. 



FIG. 101. 



The simplest piece of apparatus for measuring torsional 

 strains directly is an arrangement similar to that indicated 

 by the diagram on Fig. 101. Here S is the specimen 

 which is being twisted, and whose angle of twist it 

 is required to measure. This measurement is made 

 on a certain definite length of the parallel part 

 of the bar E F. A graduated disc or sector A 

 is fixed to one end of this length, and a radial pointer B 



