MEASUREMENT OF TEMPERATURE. 
205 
mended, but the wire gave way again below 100° G. It was, therefore, decided to 
try by a slightly different method, and in particular to protect the wire from strain. 
Some difficulty was found at first in fusing the fine tin wire on to the copper 
connecting wires. Solder was evidently inadmissible if the experiments were to be 
pushed up to the melting point of the tin. 
The tin resistances, calculated from the formula 
R/R 0 = 1 + -004323* + ’00000260£ 3 , whence Rj/Ry = 1‘4583, 
for purposes of comparison, show that, as might be expected, the observations between 
0° and 100° are very consistent and continuous. It is probable, however, that, as the 
last observation seems to indicate, the simple formula will only represent the observa¬ 
tions well between narrow limits. 
Other formulae for tin are :— 
Benoit R/R 0 = l+*004028*+ , 000005826* a , whence Rj/Ry = 1-4611. 
Matthiessen : — R 0 /R = 1 — -0036029(5+-000006136^, whence R 1 /R 0 = 1 '4262. 
Effect of heating Wire in a Bunsen Flame. 
A small spiral of the standard platinum wire was made, having a resistance of 
about 1 ohm, and its ends fused on to short lengths of stouter platinum, and these on 
to thick copper leads. 
Resistance of the whole, cold, at 16 o, 0 C., 1"0496 B.A. 
Resistance of copper connexions, about - 0140 B.A. 
The fine coil was raised to a bright orange (in full daylight) by being immersed in a 
solid Fletcher gas flame; its resistance varied slightly on either side of 4"81 with 
varying draughts of air ; half the thick platinum was heated red-hot. This was 
continued for about an hour. When the whole had cooled again to the temperature 
of the air, which had risen to 1G°'2 C., the resistance was measured, and found to be 
1 0502 B.A. The increase is almost exactly accounted for by the higher temperature. 
Readings were then taken for some time with the coil in various parts of the flame, 
and with different states of flame, with the following approximate results :— 
Description of flame, and part employed. 
Resistance 
observed. 
Temperature calculated by empirical formulm 
pt 
M 
(fi) 
(e) 
Flame burning feebly, solid just 1 
enough to cover the coil j 
Gas full on, flame I Edge of flame 
very large and solid J Centre of flame 
•T77-4-78 
4-86-4-87 
4-65-4-67 
1085 
1110 
1050 
1190 
1230 
1160 
1280 
1320 
1240 
1503 ! 
1571 
1435 
