112 
for 
Dr. Matthiessen on an Alloy which may be used 
(a2) N=15:059 —0:01077 ¢ + 0:00000722 72, 
(6) X=15-052—0-01074 ¢ + 0:000007 L4 2?. 
(ce) N=15°152 —0:01098 ¢ + 000000774 2?. 
Table VI. gives the mean of the observed conducting powers, 
those calculated from the above formule, and their differences. 
Table VI. 
(a.) (d.) 
Observed | Calculated Observed | Calculated 
conducting | conducting Diff, conducting | conducting Diff. 
power. | power. ul power. power. 
0-6=15:051 | 15:053—0-:002 || 98=14-946 | 14-947—0-001 
18:7 =14:860 14°860 0:000 30°8 = 14°729 14:728+0°001 
40°3= 14-637 | 14-638—0:001 50°7=14526 | 14:526 0-000 
59°8 = 14°442 14°441+-0°001 70°4 = 14°333 14°331+0-002 
81°0=14°235 14°234+0°001 95°1=14:094 14°:096 — 0-002 
100:0 = 14:052 14:054—0°002 
(e.) 
Observed | Calculated 
T. conducting | conducting Diff, 
power. power. 
8°2=15°063 15063 0:°000 
32°5 = 14°800 14°803—0:003 
51°5=14°608 147608 0:000 
73°3=14°391 14°389-+-0:002 
96°7 =14'162 147162 0:000- 
If we now take the conducting power at 0° = 100°3, being 
the mean of the observed conducting powers (see Table II.), 
we find 
for (a2) X=100°3—0-07216 ¢+0:0000484 7, 
(6) X=100°3—0:07196 ¢+0:0000478 7, 
(ce) N=100°3—0:07247 ¢+0:-0000511 7; 
and taking the mean of the mean of a and 0 (this being the same 
wire) and c, we find the conducting power of the annealed wire 
at different temperatures 
= 100°3—0:07226 ¢ 4+ 0:0000496 72. 
The next step was to determine the conducting powers 
of hard-drawn wires for different temperatures: but here we had 
to contend with great difficulties; for when a hard-drawn wire 
is heated to 100°, a different conducting power is generally 
found on cooling; and to obtain concordant results, it is neces- 
sary to heat the wire several times ; but when once obtained, the 
values found will remain the same, no matter how often the wire 
may be heated, showing that the apparatus and method are not 
