IN CYLINDRICAL CONDUCTORS, ETC. 
75 
cent, a linear increase of resistance with temperature, this increase agreeing with the 
temperature coefficient of copper. The fifth group, that corresponding to the spacing 
6-4 cm., is low. The discrepancy is removed if we suppose the measured resistance in 
error by 4 per cent. (0-0004 ohm). 
In the following tables the ratio of alternating current resistance R' to the direct 
current resistance R has been calculated from formula (48) and compared with the 
observed value. This ratio is not independent of the temperature as the eddy-current 
resistance varies with temperature in a different way to that of the direct current 
resistance. The value of z has been calculated using that value of R which corresponds 
to the temperature of the observation as deduced from fig. 5. 
Tables comparing observed values of the effective resistance of tw r o parallel wires 
with the calculated values :— 
0 — temperature of observation. 
/ = frequency in cycles per second. 
It = direct current resistance. 
R s —R = increase in resistance due to skin effect. 
R P = increase in resistance due to proximity of wires. 
R' = R s +R P = total alternating current resistance. 
Table I.—Spacing = 60 cm. 
6° C. 
23-5 
24-2 
25-0 
25-6 
26-2 
27-1 
27-4 
27-9 
/ . 
60 
306 
888 
1600 
2040 
3065 
3950 
5000 
fRs/R. 
1-0047 
1-108 
1-560 
2-045 
2-270 
2-708 
3-030 
3-372 
Calculated^ R P /R 
Negligible 
— 
— 
— 
— 
— 
— 
— 
[R'/R . 
1-0047 
1-108 
1-560 
2-045 
2-270 
2-708 
3-030 
3-372 
Observed R'/R . 
1-0038 
1-111 
1-587 
2-042 
2-279 
2-694 
3-034 
3-361 
Difference per cent. . 
+0-1 
-0-2 
-1-4 
+0-2 
-0-4 
+0-5 
-0-1 
+0-3 
Table II.—Spacing = 20 cm. 
6° C. 
17-2 
15-2 
15-2 
15-0 
14-9 ■ 
15-2 
15-4 
15-3 
15-4 
/. 
60 
288 
868 
1663 
2061 
3063 
3112 
3860 
5040 
r R s /R 
1-0048 
1-106 
1-578 
2-120 
2-328 
2-775 
2-790 
3-075 
3-472 
Calculated^ R P /R 
0-00004 
0-0006 
0-002 
0-002 
0-003 
0-003 
0-004 
0-004 
0-004 
ffit'/R 
1-0048 
1-107 
1-580 
2-122 
2-331 
2-778 
2-799 
3-079 
3-476 
Observed R'/R 
1-0058 
1-106 
1-584 
2-120 
2-313 
2-755 
2-781 
3-067 
3-446 
Difference per cent. 
-0-1 
+0-1 
-0-3 
+0-1 
+0-8 
+0-8 
+0-5 
+0-4 
+0-9 
m 2 
