INSTRUMENTS USED IN ENGINEERING LABORATORIES, 



499 



Committee. The measurements have taken much time, and the whole 

 oi. the reports of observers have not yet been received. Some of those 

 ah-eady sent reached the Committee too late for discussion this year. It 

 appears, therefore, to the Committee that it is unavoidable that only an 

 interim report can be presented this year. The Committee ask for re- 

 appointment, in order that the results obtained may be discussed and 

 presented. 



It may, however, be useful even at this stage, to give a very short 

 summary of some of the results sent in. The following table gives a 

 summary of the measurements of the standard bars by different observers. 

 It will l)e seen that there is an appreciable difference even in the measure- 

 ment of the dimensions of the same bar. The fiat bar, it may be noted, 

 was machined on the edges only. 



Ifeasurements of Dimensions of Test Bars. 



The following table gives the values of the coefficient of elasticity for 

 the greatest range of stress observed for each bar. The values are given 

 for the first and second loading of the bar, and also the mean of the two 

 observations. It will be seen that, even for the mean of two sets of 

 readings, over the greatest range of stress the elasticity of the bar permits, 

 there are very appreciable differences in the values ol^tained. It remains 

 to be considered in a more detailed discussion of the results whether any 

 evidence can be found as to the source of the discrepancies. It may be 

 due to error of the testing machine, to error of magnification by the 

 extensometer, or to error of calibration of the extensometer. It is just 

 possible it may be due in part to temperature or other action independent 



of both testing machine and extensometer. 



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