118 



EW INC KXTENSl >METKH. 



inch. This instrument is easily calibrated either by 

 of a vernier caliper or a measuring machine. Besides brin- 

 simple and inexpensive to make, it is easily manipulated 

 und very reliable in its readings; the writer can state this 

 from his own experience. It should be mentioned that 

 the pointer is made of wood, 



A general view of this instrument is shoAvn in Fig. 47. 



B 



B 



Fig. 48. 



67. Ewing Microscope Extensometer.* In this 

 extensometer, instead of the extension of the bar being 

 magnified by mechanical means in the form of a lever, 

 as is the case with the Kennedy instruments, this is effected 

 by the use of a microscope fitted with a micrometer scale. 

 A diagrammatic view of the instrument is shown on Fig. 

 48. In this figure the test bar is marked A. At two 

 points on the bar 0, O, ten inches apart, are fixed, by 

 means of pairs of set screws, two separate pieces B and C. 



* Proceedings Physical Society, May, 1895. 



