254 DESCRIPTION OF AUTOGRAPHIC STRESS-STRAIN APPARATUS. 



the wire at the same level as the knife edge of the steel-yard (in 

 order to eliminate the effect of the moment of the tension in the 

 wire about the fulcrum of the steel-yard) and round a small drum 

 U attached to the rider from which the poise weight is suspended 

 by means of a bracket. The wire on the drum is wound in or 

 payed out by means of a handle on the drum which is controled 

 by a small friction brake. There is a strong clock spring inside 

 the drum, so fixed that the revolution of the drum produced by 

 winding the poise weight along the steel-yard is made to coil up 

 the spring, and by winding the poise weight in the reverse direction 

 the spring uncoils and brings back the drum to its original position. 

 Thus the drum is made to revolve through an angle which is 

 proportional to the distance through which the poise weight has 

 been wound, and therefore proportional to the load on the specimen. 



The deflection or compression as the case may be, is transmitted 

 and recorded upon the revolving cylinder in the following manner : 

 A steel rod H, square for a portion of its length, slides freely in 

 bearings provided in the end plate frames, and also at the extremity 

 of an overhanging bracket, the rod carries a slotted link in which 

 slides a small roller which is pressed against the sides of the link 

 by the movement of the lever N. There is also a weighted pencil 

 which can be adjusted and fixed to any position of the square rod 

 between the end plates of the frame. The lever N, is provided 

 with knife edges which are pressed by the forked end of the 

 screwed rod S, as the specimen yields. The rod S, slides or is 

 fixed in a bearing which is attached to the test specimen in the 

 manner shown on Plate 2. 



In the compression tests the screwed rod S, is attached by 

 means of a union screw to a steel rod which is connected at its 

 other end with the fixed compression block of the machine. The 

 length of the rods is arranged according to the length of the 

 specimen tested. Both in cross-breaking and in compression the 

 yielding of the specimen is transmitted to the. knife edges of the 

 lever N, as a simple harmonic motion which is reproduced 

 multiplied ten times on the sliding rod H, carrying the pencil M, 

 in the manner already referred to. 



A piece of sectional paper is wrapped round the cylinder and 

 clipped, upon which the diagram or diagrams are drawn in the 

 following manner : — The pencil is adjusted to the datum point on 

 the paper by means of the adjusting screw T, and the adjustable 

 connection of the steel wire with the poise weight. The force 

 pump is then worked until the load upon the specimen is sufficient 

 to raise the steel-yard and the poise weight suspended from it, 

 which causes the specimen to yield and the pencil to draw a line 

 parallel with the axis of the drum. The pumping is continued 

 and the poise weight wound along the steel-yard keeping it 



