as a Standard of Electrical Resistance. 113 
faulty, whether by letting the wire remain for a length of time 
it will gradually assume its original conducting power or not is 
a question now under consideration. With annealed wires this 
is also the case, but in a much less degree. All the above 
wires, as well as the following, were heated several times before 
concordant results were obtained. I cannot at present state 
the cause of this behaviour; but experiments are now being 
made on the subject by Dr. von Bose and myself. 
Hard-drawn wires of No. 5 (a) and No. 3 (8) alloys were 
heated, (a) in a glass tube in a water-bath, (4) in an oil-bath. 
The values found are given in Table VII. 
Table VII. 
(a.) (d.) 
| 
Conducting Conducting 
power. power. 
0°0=15°075 9°3=14°870 
20°9=14°858 35°6 = 14:608 
46:5 =14°605 50°8 = 14°460 
76°4=14°318 67°6=14:300 
100°0=14:094 98:1=14°011 
71°6=14°370 70°-4=14:278 
51°4=14°566 54:4 = 14°426 
23°8 = 14°838 35°2=14°613 
0°0=15:075 14°1=14°824 
The diameter of (a) was 0°616 millim., and its length 876 
millims., and that of (6) 0°551 millim., and its length 348 millims. 
Taking, as before, the mean of the two temperatures and con- 
ducting powers, and calculating the values of w, y, z from them, 
we find 
for (2) X=15:074—0-01012 ¢+0°00000829 7, 
(6) X=14°964—0-01011 ¢+0°00000410 22. 
Table VIII. gives the mean of the observed conducting 
powers, and those calculated from the above formule, with their 
differences. 
Table VIII. 
(a.) (d.) 
Observed | Calculated Observed | Calculated 
conducting | conducting conducting | conducting 
T. power. power. Diff. T. power. power. Diff. 
0°0=15°075 15:074-+-0:001 11:7=14°847 14:847 0-000 
22°3=14°848 14°850—0-002 35'°4=14°610 14°611—0°001 
49:0 =14:586 14°586 0°000 52°6 =14°443 14443 0°000 
74°0=14:344 14°343-+-0°001 69°0= 14:287 14°286+0:001 
100°0 =14°094 14:095—0:001 98:1=14°011 14011 0-000 
Phil. Mag. 8. 4. Vol. 21. No. 138. Feb, 1861. I 
