IN'STKUMENTS USED IN EXUIXEERIXG LABORATOlUEt-. 



497 



Calibration of Instruments used in Ungineenng Laboratories. — JReport 

 of a Committee^! consisting 0/ Professor A. B. W. Kennedy, F.R.S. 

 (Chairman), Professor J. A. Ewing, F.R.S. , Professor D. S. 

 Capper, Professor T. H. Beare, and Professor W. C. Unwin, 

 F.B.S. {Secretary'). (Drawn itp by the Secretary.) 



At the first meeting of the Committee it was decided to investigate 

 initially the accuracy of instruments for measuring the tension coefficient 

 of elasticity, or Young's Modulus. A general letter was addressed to 

 various professors and others in charge of engineering laboratories inviting 

 co-operation. Most of those written to agreed to make a series of measure- 

 ments for discussion by the Committee. 



It was then decided' that sets of standard test bars should be prepared, 

 to be subjected to tension and measurement. Figs. 1, 2 show the forms 

 of test bar decided upon. Two of the standard bars of each set are cylin- 

 drical bars, with screwed ends of about 1^-inch and f^-inch diameter. 

 These have gauge points for measuring instruments, suitable for extenso- 

 meters of 8-inch, 10-inch, 16-inch, or 20-inch range. These bars are of 

 a special steel of high tenacity, rolled specially for the Committee by the 

 Blaenavon Company. The whole of the bars were cut from a single 

 rolled bar about 20 feet in length, and were very accurately turned to the 

 required dimensions by Mr. W. R. Munro. The third bar of each set was 

 a flat bar, of section about 2 inches by ^ inch, of mild steel. All these 

 bars were cut from a single plate, and they were prepared with gauge 

 points at 8 inches and 10 inches. 



In order to obtain some preliminary information as to the mechanical 

 properties of the standard bars, one round bar and one flat bar were 

 tested in the testing machine at the Central Technical College. The 

 following table gives the results obtained : — 



Preliminary Tests of Materials used for Standard Bars. 

 Texsiox Experiments. 



I 



Bar D was exactly similar to the flat bars A, B, C. 



Ear N was of the same steel as standard bars marked E, F, K, L, &c. 



The Committee then drew up a test-sheet form to be issued with the 

 bars, on which measurements were to be recorded. These sheets were so 

 arranged that two sets of measurements for each bar, and the mean 

 of these, should be recorded ; also that the extensions for short and 

 long ranges of stress should be recorded. It was hoped that in this 

 way some measure of instrumental errors would be obtained. 



In January two sets of bars were sent out for measurement, to be 

 circulated amongst those who had consented to cooperate with the 

 189-5. K K 



