210 
IOWA ACADEMY OF SCIENCE 
Vol. XXIV, 1917 
Fatigue . — One short set of experiments was made to test the 
effect of fatigue on the value of n. A small effect was found, 
and in the usual direction, that excessive vibrations lower the 
rigidity, which may be recovered by permitting the wire to rest. 
Table I will make this point clear. This result is just opposite 
from that found for platinum-iridium wires by the author . 3 
With such wires the effect of continued vibrations was to raise 
n, and the effect of rest was to lower its value. 
TABLE I. 
EFFECTS OF FATIGUE. 
To 
f 
T n 
“n” (from T n ) 
Remarks 
6.778 
6.670 
11.28 X 10U 
1 
From rest 
6.796 
6,686 
11.23 
Vib. 30 min. 
6.791 
6,678 
11.26 
Rested over night 
6.815 
6,704 
11.17 
Vib. 60 min. 
hi General.-*— It may seem that the range in the values for n 
for a given pure substance like tungsten is excessive, but further 
consideration will make it appear a matter that should cause 
small surprise. Elastic constants are no doubt complicated func- 
tions of the treatment and history of the wires considered, hence 
depend on their crystalline structure, and not primarily upon 
their chemical constitution. It is easily understandable that great 
stresses are involved in the drawing of these wires- — sudden heat- 
ing and cooling, for example — and no doubt the surface is in a 
state of different crystal aggregation than is the interior. For 
the few wires experimented with, counting the ones used in the 
preliminary investigations, the range iu value for n has been 
from 9.49 to 16.2X10 11 dynes per cm. 2 , or a variation of 71 per 
cent. Even a greater range might have been found had more 
specimens of wire been at hand. This is not greater than some 
values for other substances which I have selected from Winckel- 
mann’s Handbuch d. Physik, and incorporated in Table II*. 
There is no such thing as a definite coefficient of rigidity ac- 
companying a definite chemical composition. Its value depends 
more, in fact, upon the manner of drawing, and the recent his- 
3 Phys. Rev. 31, p. 421, 1910 ; Proc. Iowa Acad. Science, XVIII, p. 115, 1911. 
