480 KEPORTS ON THE STATE OF SCIENCE. — 1919. 



four self-contained, double-lever, strain-measuring units. A scale 

 division represents about three-milliontlis of an inch change of length of 

 the specimen, but less sensitive elements are used for materials ■which 

 have low values of ' E.' The test length is usually 1*5 inches. 



Three measurements are sufficient to allow the strain distribution 

 across the section of the test piece to be calculated, but the fourth intro- 

 duces no further complication and allows a useful check to be made, or 

 avoids the scrapping of a series of readings if one element deflects beyond 

 the limit of its scale. 



Typical plottings of the four measurements against the loads are given 

 in fig. 14 as an example of very eccentric loading, and in fig. 15 to show the 

 best lesult realised in practice.. 



Variation of Strain across the Section of a Test Piece. 



The first results are collected to indicate the variation of the strain across 

 the section of a specimen. The usual precautions were observed for the 

 type of test considered. The strain distribution usually alters somewhat 

 with the load, so the figures tabulated have been taken for the region of 

 the elastic limit, or, when the load was not taken so high as this, for the 

 greatest load applied. 



