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The outer end of one of the jaws is connected to a worm-wheel, 

 the rotation to which is imparted through the worm by means of 

 the crank. The other jaw carries the pendulum, to which is con- 

 nected, a little below the jaw, the pencil which is held by a spring, 

 tight against the sides of the guide curve. This curve is made so 

 that when the pencil rolls on it, in virtue of the swinging of the 

 pendulum through the test piece, the ordinates which are recorded 

 upon a cross-section paper carried by a drum on the opposite jaw 

 or on the one connected to the worm wheel, are proportional to 

 the moments about the axis of the test piece. The machine, by 

 the tracing of a simple curve, tells all the characteristics of the test 

 piece. The circumference of the drum is equal to thirty-six 

 inches, and the inches in the paper are divided into ten equal parts, 

 thus making each inch of paper equal to 10. The vertical lines 

 are also divided in inches and each into tenths. 



When the piece is secured between the clamps, the crank is 

 turned by hand with a uniform motion and a slow rotation, inter- 

 rupted only by the rupturing of the piece, is given to it, causing 

 the pendulum to swing up on one side. This measures the resis- 

 tance to torsion of the test piece which is recorded autographically 

 in the paper. 



To make these tests, we took off the bob from the pendulum, 

 as it offers too large a moment for the torsional resistance of the 

 woods for the size of test piece used. Before making the tests, 

 we found the necessary constants of the machine to work out the 

 results of tests, as follows : The pendulum without the bob was 

 supported horizontally by a column, which rested on a scale. 

 Thus, the maximum moment of the pendulum was weighed, and 

 the corresponding ordinate in the curve observed : 



Lever arm, 48 inches. 



Weight of column with lever arm 5275 pounds. 



" supporting columns 21*5 " 



" lever arm, or pendulum 3i' 2 5 " 



Hence maximum moment, 1,500 inch-pounds. 



Maximum ordinate traced by the pencil, or ordinate corresponding 

 to horizontal position of the pendulum 4-3 inches. Therefore, 

 one inch of ordinate = 348-837 inch-pounds. 



We found the friction of the machine by means of a delicate 

 spring balance, attached at a distance of fifty inches from the 



