DESCRIPTION OF AUTOGRAPHIC STRESS-STRAIN APPARATUS. 255 



floating in a horizontal position and balancing the load on the 

 specimen. The length of the diagram may be increased by taking 

 off the weights from the rod suspended from steel-yard, which is 

 always done when small specimens are tested. 



The sizes of the pulley D and the spiral grooves have been so 

 made that the load can at once be read off on common sectional 

 paper divided into inches and tenths. 



To draw stress-strain diagrams for tension tests the frame R 

 carrying the revolving cylinder is fixed to the underside of the 

 cast iron longitudinal stays of the machine, and the lever N used 

 in the cross-breaking and compression tests is removed. A second 

 rectangular frame is attached to the upper side of the longitudinal 

 stays before referred to, see Plate 3. Three brass plates connected 

 with two springs of bent steel, one on each side of the centre plate, 

 are arranged to move slightly upwards and downwards in a vertical 

 plane between guide blocks fixed to the rectangular frame. The 

 centre plate carries the bearings which support two levers having 

 equal arms and which turn with very little friction upon conical 

 centres. The end plates are attached to the rectangular frame by 

 means of the screws W 1 and there are two screws on each side 

 W 11 which are used to raise or lower the lever frame and adjust 

 it to the size of the specimen. Two steel points are fixed one to 

 each of the levers which are pressed slightly by means of the bent 

 spring into corresponding holes in the test piece spaced 10 inches 

 apart. One of the levers carries two pulleys K and Q, the other 

 an adjustable screwed rod J. 



A fine steel pianoforte wire is attached to the rod J, and led 

 over the pulleys K and Q in the manner shown, and continued over 

 a guide pulley P the axis of which is carried by a bracket fixed to 

 to the longitudinal stays of the machine. A second axis O is 

 also carried by this bracket upon which two pulleys of unequal 

 size revolve together. The wire passes round the smaller pulley 

 and terminates with a weight S. A very fine steel wire is connected 

 to the circumference of the larger pulley and to one end of the 

 rod H which carries the pencil, the other end of the rod H is 

 connected to a balance weight by means of a similar wire passing 

 over guide pulleys Y 1 and V 11 . The smaller pulley may be % or 

 J the diameter of the larger, multiplying two or four times, 

 according to the size of the diagram required. 



The load is recorded on the revolving cylinder by winding the 

 poise weight as before. The elongation produced by the load is 

 communicated to the pencil in the following manner : — The steel 

 points of the levers resting in the small dots or holes in the test 

 piece move farther apart as the test piece elongates, and the pulley 

 K moves towards the rod J and raises the weight S, the friction 

 of the wire in the Y shaped groove of the smaller pulley on the 



