Small St-i 



Bars subjected to Twist. 



527 



rotating by pins, C, engaging with slots, S', cut in the screws. 

 The screws work in rotating nuts, D', provided with bevel 

 pinions, E', gearing with a hand-operated bevel ring, G', so 

 that all the screws are advanced or receded together. An 

 additional pinion, H7, is provided, operated by a key fitting 

 on its squared spindle, J', so that the screws are firmly gripped 

 upon the bar. The inner ends of the nuts have a collar- 

 bearing, K7, so that the stresses are borne by the body, I/, of 

 the chuck, and the bevel ring is prevented from seizing by 

 bearing-plates and an adjustable ring, W, at the back. This 

 bevel ring can be slid back to allow any screw to be separately 

 adjusted. Other modified arrangements of the chuck have 

 been tried in which the guide-pins have passed bodily through 

 slots cut through the inner ends of the screw, and the screw 

 pairs have been inverted ; but these modifications have not 

 answered well. 



An example of tests made with this form of apparatus is 

 appended, the same Bessemer steel bar being used. 



Mean value of calibration-test — 1 minute of arc corresponds 

 to 36 divisions of scale. 



Length under measurement 8 inches, diameter 0*747 inches, 

 torsion-arm 15 inches, a constant. 



Load, 

 lbs. 



Reading. 



Differences. 







1 



800 

 759 

 718 

 677 

 636 

 596 

 555 

 513 

 471 

 430 

 389 

 349 

 309 

 267 

 225 

 183 

 143 

 103 

 62 



41 

 41 

 41 

 41 

 40 

 41 

 42 

 42 

 41 

 41 

 40 

 40 

 42 

 42 

 42 

 40 

 40 

 41 



2 



3 



4 



5 



6 



7 



8 



9 



10 



11 



12 



13 



14 



15 



16 



17 



18 





And we have for this test-bar = 11,850,000 lb. per square 

 inch. 



A second test gave very approximately the same result. 

 Angular displacements of \" can be measured with this form 

 of apparatus. As the overhanging arm carrying the micro- 



202 



