128 
PROF. W. E. DALBY: RESEARCHES ON THE ELASTIC 
begins at the origin, so that the extension is increasing at a greater rate than the load 
from the commencement of loading. There is no definite yield point. 
The most interesting result to notice is that the test piece goes on 
shrinking in length after the load has been removed. It is shrinking under the 
action of its own internal molecular forces because it is entirely free from external 
load. 
The shrinking at no load is indicated by the flat bottom of the loop. A dwell of 
1+ minutes was made in the experiment after the removal of the load and before the 
re-application of the load. All the perceptible shrinking at no load takes place 
within this time interval. 
At the third loop after the load was removed the light was shut off and flashed on 
at intervals of ^ seconds to get some idea of the rate of shrinking. 
Tin. —Fig. 13. Diameter of test piece 0'8 inch. Gauge length 5 inches. This 
Fig. 13 (tin). 
test piece was turned from a bar of tin. It exhibits properties similar to zinc 
on a smaller scale. There is shrinking continuing for about 1 minute after the 
load has been removed, and there is the same absence of a proportional elastic 
line. 
Copper .—Pure and free from arsenic. Fig. 14. Diameter of test piece 0‘8 inch. 
Gauge length 5 inches. There is no marked limit of proportionality and no yield 
point in this material. The noteworthy feature of the record is the small rate of 
increase of loop area. This small rate of increase of loop area is a common 
