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IV. Researches on the Elastic Properties and the Plastic Extension of Metals. 
By W. E. Dalby, F.R.S., Professor of Engineering at the City and Guilds 
( Engineering ) College of the Imperial College of Science and Technology. 
Original Paper received January 28,—Revised form March 24, 1920. 
§ 1 . Preliminary. 
On March 7, 1912, I described an instrument which gives photographically a 
load-extension diagram of a metal test piece during the process of stretching it to 
fracture. 
On February 13, 1913, I described further experiments with the instrument .* A 
diagram was shown which was taken from a test piece broken in ten seconds. It is 
safe to say that up to that time no apparatus existed which would give a complete 
record of the load-extension relation during such a quick break. 
I have since that time arranged the apparatus to record at even a quicker rate. 
Fig. 1 shows the record of a break done in 2 ‘15 seconds. The test piece measured 
Fig. 1 (mild steel). 
one inch between the shoulders. The line of the record is in dashes. These dashes fix 
the time scale of the diagram. Centre to centre of a pair of dashes corresponds to 
* Additional results are given in 1 Transactions of the Institute of Naval Architects,’ March 29, 1912, 
‘Institute of Metals,’ May Lecture, 1917, vol XVIII., No. 2. 
VOL, CCXXI. A 585, S [Published September 29, 1920. 
