Coefficient of Expansion of Incandescent Platinum. 865 
The following table gives the results of the measurements, 
for temperatures ranging between 0° and a point not far below 
the melting point of platinum. Both resistance and length of 
wire at 0° are taken equal to unity. 
Tasize IL. 
Resistance. Length. Resistance, Length. 
1-0060 100000 3°7090 1°01229 
10410 1:00002 3°7427 1°01223 
15071 1°00125 3°7813 1°01285 
19000 — 1:00289 3°8750 1701349 
2°1212 1°00380 3°8904 101371 
2°2934 1:00456 3°9305 1°01378 
2°3035 1°00489 4°0303 1°01450 
2°7821 1°00732 40631 1:01469 
2°8633 1°00763 4°0655 1701495 
2°9696 1°00809 4°0747 101499 
3°3533 1°01022 40841 101514 
3°3741 1-01003 41248 101540 
3°4151 1°01042 4°2005 101567 
3°6449 1701160 4°2447 101632 
IIT. Dr. Siemens has pubilabad three formule for the varia- 
tion of the resistance of a platinum wire with the temperature. 
temperatures were calculated in one case (formula a) 
from the heating effect of a mia vin spe the taped heat id 
mometer. 
These formule are: 
(a) r=039369 T?+-00216407 T—-24127 
(6) r="0021448 T? +-0024187 T+ 30425 
(c) r='092183 T~+-00007781 T+ 50196 
where T is the absolute temperature and r the resistance of the 
wire. The following formula by Benoit is ake sometimes 
used for the determination of high temperature 
(d) r=1+4 002445 ¢+ 000000572 @. 
3 this expression ¢ denotes the temperature in degrees centi- 
rade, 
When as is frequently the case, it is more convenient to 
measure the length of a wire than its resistance, we may employ 
Matthiesen’s Pacien 
(e) 1=1,(1 + 00000851 ¢+-0000000035 ¢’) 
