CAST-IRON BEAMS. 18% 



after being carefully measured, is placed in the machine 

 with one of its narrow faces resting on the supports. The 

 deflectometer is now fixed in place, care being taken that 

 the points of attachment of the instrument coincide with 

 the neutral surface of the beam, and that the two outer 

 points are exactly over the points of support. When the 

 pointer of the deflectometer has been set to the zero of its 

 scale the test may proceed. In the case of a cast-iron beam 

 of this size, it will be found convenient and sufficient to 

 take deflection readings at increments of 50 Ib. It will be 

 seen, on referring to the table of figures, that readings are 

 recorded at every 50 Ib. up to l,5001b., and after that at 

 intervals of 200 Ib. The meaning of this is that the read- 

 ings at the small intervals were taken with the deflecto- 

 meter. After this the instrument was removed, and direct 

 measurements made with a steel rule from a frame like 

 that shown on Fig. 83, page 174, or from the frame of 

 the deflectometer itself. By thus removing the instrument 

 before the point of fracture is nearly approached it is 

 saved from any damage that it might suffer if the beam 

 fractured when it was in place ; and, moreover, the 

 readings obtained up to this point are quite sufficient 

 for the purpose required. Great care should be taken that 

 the second series of measurements are continuous with the 

 first. 



