380 
Proceedings of the Royal Society of Edinburgh. [Sess. 
along a plane normal to the axis. Rupture should commence when the 
axial tensile stress is equal to the cohesion K, but one would expect the 
value of this final stress to be somewhat less than K on account of the fact, 
of which evidence has been given by the writer elsewhere,* that fracture 
usually begins in the centre of the cross section of the bar, suggesting 
some concentration of stress here. 
In the table given below, some values of K, calculated from the yield 
points obtained for steel bars tested in tension, are compared with the final 
stresses carried by the bars at the instant of fracture, the final stress being 
calculated for a normal cross section taken through the place where 
rupture commenced. These figures have been chosen at random from a 
number of results, and the bars were not tested specially to check the value 
of K. The values of both yield point and breaking stress were not taken 
with extreme accuracy; in fact, to obtain a true value of the breaking 
stress is not an easy matter, as the lever of the testing machine must be 
exactly balanced at the instant of rupture. Moreover, the measurement of 
No. 
Yield point — t. 
xr _ 3*384 t 
Stress at rupture. 
Reduction of Area 
Tons per sq. in. 
JLA U t/UTI V • 
Tons per sq. in. 
per cent. 
Round Bars, originally f inch Diameter. 
6060 
17-0 
57*5 
54T 
61*3 
6170 
16-0 
54*2 
56*7 
63-5 
6321 
17*0 
57-5 
59-7 
64-0 
6323 
17-0 
57-5 
53-6 
59-7 
6324 
18-0 
60-9 
56-9 
61-6 
6337 
17-0 
57*5 
56-8 
634) 
6729 
20-0 
67-7 
59-7 
62-7 
6730 
200 
67*7 
65-5 
61*5 
6765 
19*5 
66-2 
56-8 
62-9 
6942 
23-0 
77-9 
55-2 
41-3 
6944 
23-0 
77-9 
65-0 
54*2 
7346 
18*5 
62*5 
51-0 
54-4 
7354 
19-0 
64-3 
58-2 
64-6 
Flat Bars, originally 1| inches wide and \ inch 
THICK. 
6052 
16-0 
54-2 
52T 
47-2 
6062 
17-0 
57*5 
50*9 
52-6 
6202 
16-0 
54*2 
53-0 
58-0 
6215 
13-0 
44-0 
46-5 
5T0 
6437 
14-0 
47-4 
50-5 
57-0 
6440 
16-5 
55-9 
50-8 
543 
6441 
16-0 
54-2 
41-6 
45-8 
6731 
16-0 
54-2 
46-4 
51T 
6732 
17-0 
57-5 
54-0 
56-5 
1 
* Loc. cit ., p. 146. 
