364 Kohlrausch and Loomis—Influence of Temperature 
versally at the temperatures of about —10°, +15° and +80°. 
Unfortunately, however, very long intervals. (at least a year) 
occur between the observations, and it would seem that he did 
not race employ the same bars, so that his inv pagog a 
but a limited conclusion in regard to the 
qeemtions of elasticity as modified by temperature. Finally, the 
dilatation caused by sion was disregarded in the nu- 
merical values given b er, a source of serious errors in 
view of the method of oat which was employed. 
A few of the results derived by Kupffer were obtained by 
means of torsional vibrations. Among these are the coeffi- 
cients of temperature for the elasticity of an iron wire (piano 
cord), of a copper wire and of a brass wire. After having 
applied to these values the correction required for the dila tation 
of the vibrating disc, the decrease of the elasticity for 1° ex- 
pressed in parts of the total elasticity is found to be 
for iron, 0°00055 (“ mem.” Sebi 
* copper, 0°00082 S. 4 
“> Drees, 0°00039 ( S. 467 7) 
These values agree tolerably well with those found by us, with 
the exception of the copper wire, in regard to which it is pos- 
sible that the divergence may be caused by the ehh" 
that we employed a chemically pure metal. 
. The absolute moduli of elasticity of the iron, copper and brass 
wires calculated from torsional vibrations and from the velocity of 
soun 
To determine from our investigations the absolute moduli of 
torsional elasticity, it is necessary to know the dimensions and 
mass of the wires, as well as the moment of inertia of the vi- 
brating weight. 
_ The latter is to be calculated from the mass of 7 or 
lead cylinder =1818 grs. and the interior radius = and 
the exterior radius =5-07 c.m. It is found to ie 
1818 owes 
(507 5°07 ee ere 0°34 )=: 23470 grs. Oo c.m. 
To this must ‘. added the moment of inertia = 40 fa 
of the connecting pieces and the mirror, which was calculated 
from their size and form. The total moment of inertia there- 
0 
ore is K= 23510 ers. 
Further was determined 
Tron. Copper. Brass. 
The length of the wire, l=20°80 20°75 =. 20°80 c. m. 
The mass of one c. m. length, m=0-00301 0°00655 0-00403 grs. 
The densi A=7°82 9-00 8°41 
The time vibration at 20°, t==17'35 . 12:23 .. 20°55 sec. 
radius of the wire, r=0°0111 0°0152 0°0123 ¢. m. 
