DEFLEC'TOMETERS. 



175 



Here the beam to be tested, marked S, is shown supported 

 at the two ends, and having the load applied in the centre. 

 B represents a light but sufficiently stiff frame, held to the 

 bottom of the beam by means of spring clips. As the loads 

 on the specimen increase, it will be bent, but the measur- 

 ing frame will retain its original shape. The measurements 

 of the deflections may be determined by applying the steel 

 rule, R, and taking the deflections direct. The measuring 

 frame may be made of either metal or wood ; if of the 

 latter, a small plate of brass should be affixed to it so as to 

 provide a sharp edge, or a line, to measure from. 



Strictly speaking, the measuring bar, the points of 

 support of, and the point on the beam from which the 

 measurements are taken should be in the neutral axis of 

 the beam, as it is in reality the deflection of this that is 



FIG. 84. 



FIG. 85. 



wanted ; but it is more convenient to attach it loosely to 

 the surface of the beam, especially as, if the bar is attached 

 this way, there is less likelihood of its being broken 

 when fracture takes place and the two parts of the 

 beam fall to the ground, and the error involved is rela- 

 tively small. A more permanent measuring apparatus 

 than that described may be arranged by having the steel 

 rule attached to the measuring bar during the test. 



Provision is made on some of the Buckton-Wicksteed 

 machines for measuring the deflections of beams by 

 means of a plate, A (Fig. 84), supported below the beam 



