4 
DE. A. MATTHIESSEN AJfD M. VON BOSE ON THE INELUENCE OF 
have a higher conducting power when hot than cold, yet in either case it is so infinitely 
small, that it cannot influence the results obtained in the manner just described. 
Again, it was proved in a former research* that the formula for the correction of 
conducting power for temperature of a wire, deduced from the observations made in an 
oil- or air-bath, were exactly the same. Thus the formula obtained for an annealed 
wire of the gold-silver alloy heated in the oil-bath was 
x=15-052-0-01074!^+0-00000714f, 
and that for the same wire heated in an air-bath was 
A=15-059-0-01077^+0-00000722f. 
As, however, more accurate results may be obtained by experimenting in an oil- than 
in an air-bath, on account of the wires taking more readily the temperature of the bath, 
and of their being more rapidly cooled if heated by the current passing through them, 
we have chosen this manner of heating the wires in preference to the other. 
As oil, and more especially oil when hot, attacks most wires to a degree which would 
render the observations valueless, we were obliged to varnish them. The best varnish 
for the purpose is a solution of shell-lac in alcohol. For instance, a hard-drawn copper 
wire, not varnished, loses in conducting power after having been heated in an oil-bath 
to 100°, but if varnished, increases. To show that varnishing has no effect on the 
results, we give in Table I, the conducting power of a hard-drawn gold wire, first not 
varnished, and then varnished. Each result is the mean of two observations. 
Table I. 
Not varnished. 
Varnished. 
Conducting power. 
Conducting power. 
T. 
Difference. 
Difference. 
Observed. 
Calculated. 
T. 
Observed. 
Calculated. 
15-30 
72-697 
72-705 
— 0-008 
13-85 
73-120 
73-085 
+ 0-035 
30-55 
68-806 
68-879 
-0-073 
30-95 
68-756 
68-782 
— 0-026 
48-65 
64-659 
64-717 
-0-058 
49-55 
64-523 
64-520 
+ 0-003 
69-55 
60-409 
60-423 
— 0-014 
68-40 
60-636 
60-645 
-0-009 
83-25 
57-915 
57-906 
+ 0-009 
84-55 
57-704 
57-680 
+ 0-024 
99-85 
55-151 
53-174 
— 0-023 
98-70 
55-346 
55-352 
-0-006 
84-55 
57-704 
57-680 
+ 0-024 
84-90 
57-645 
37-620 
+ 0-025 
70-80 
60-224 
60-184 
+ 0-040 
70-25 
60-318 
60-289 
+ 0-029 
50-85 
64-239 
64-239 
0-000 
31-20 
64-149 
64-164 
-0-015 
30-95 
68-746 
68-782 
-0-036 
30-60 
68-886 
68-866 
+ 0-020 
16-80 
72-343 
72-316 
+ 0-027 
17-85 
72-111 
72-045 
+ 0-066 
The formula deduced from the observations, and from which the conducting powers 
were calculated, was 
X=.76-838-0-27973iJ+0-0006285^^ 
The thermometers used were: — 1. One divided into degrees, each of which was 3*5 
* Philosophical Magazine for February 1861. 
