196 
DES. A. MATTHIESSEN AND C. YOGT ON THE INFLUENCE OF 
Table XXV. 
Metal. 
Observed percentage 
decrement in the 
conducting-power 
between 0° and 100°. 
Conducting-power at 0°. 
Mean. 
Observed. 
Calculated 
for the pure metal. 
Platinum (1) 
21*45 
11*72 
17*79 
Platinum (2) 
20*73 
11*53 
18*28 
j 18*03 
Palladium (3) 
24*01 
13*99 
18*35 
Palladium (4) 
2209 
1268 
18*54 
> lo*44 
Magnesium (5) 
26*89 
36*82 
41*50 
l 4447 
Magnesium (6) 
28*72 
39*66 
40*85 
r 1/ 
Aluminium (7) 
28*19 
54*07 
57*01 
1 5606 
Aluminium (8) 
26*10 
46 95 
55*12 
> 
[It is scarcely necessary to add, that in the same manner as the formulae for the cor- 
rection of conducting-power for temperature may in most cases be deduced where the 
composition and conducting-power of an alloy at any temperature are known, that for 
the correction of the conducting-power for temperature of an impure metal may also be 
calculated, using the conducting-power of the annealed metal for X' 0 , Xj, X' 100 . This is of 
practical importance ; for in testing copper wire for telegraphic purposes, the formula for 
the correction of its conducting-power for temperature may be easily deduced, of course 
only in cases where the conducting-power is within the limits above stated. It has 
already been elsewhere shown that the conducting-power of commercial metals, copper 
for instance, varies considerably according to the state of its purity. Thus a specimen 
of Rio Tinto copper was found to conduct as follows : — 
Length 398 millims. ; diameter 0*331 millim. 
Conducting-power found before „ Reduced to 0°. 
heating the wire 13*480 at 16*6 13*622 
Ditto, after heating to 100° for 
1 day 13*473 at 16*9 13*586 
Ditto, for 2 days 13*442 at 14*9 13*573 
Ditto, for 3 days 13*420 at 15*7 13*558 
Ditto, for 4 days 13*418 at 16*0 13*558 
T. 
Conducting-power. 
14*67 
13*429 
57*33 
13*064 
100*00 
12*713 
X = 13*558 - 00088326^-f 0 000003844?;- 
which corresponds to a percentage decrement of only 6-23, whereas the conducting-power 
of pure copper decreases between 0° and 100° C. 29*69 per cent. — Feb. 1864.] 
Table XXVI. contains a list of the conducting-powers of metals in a pure state. 
Those marked with a f are those deduced from the impure metals, and they may be 
called the probable values for the conducting-powers of annealed wires of the metals. 
