21 



The torsion tests were made in the autographic testing machine 

 of Prof. Thurston : It consists of two angle frames united at 

 their vertices by a cast-iron rod and rigidly bolted to a heavy cast- 

 iron bed, thus making the machine very firm. These two angles 

 have the bearings in line with the jaws or wrenches which hold 

 the piece to be tested by means of steel wedges put from opposite 

 sides. The test piece is put in line before securing it rigidly 

 between the jaws, by means of centres in each jaw, one resting on 

 a spiral spring and the other turned by a screw which projects out 

 of the frame, thus enabling to place the piece symmetrically and 

 directly in line with the axis of rotation. 



