392 
MESSRS. W. E. AYRTON AND H. KILQOUR ON THE 
Table IX. —continued. 
Diameter, 1’2 mil, or 0‘031 millim. Length, 2500 centims. Water-jacket, 10 o, 5 C 
April 13th, 1888. Fig. 12. 
Current, 
in amperes. 
P.D., 
in volts. 
Resistance, 
in olims. 
Equivalent 
temperature of 
wire. 
Emissivity. 
0-01026 
0-31863 
31-062 
O 
130 
•001301 
0-02052 
0-64035 
31-212 
14-54 
•003236 
0-03077 
0-96618 
31-396 
16-5 
•004930 
0-04103 
1-3054 
31-814 
20-8 
•005173 
0-06155 
20177 
32-782 
30-4 
•006208 
0-08206 
2-7598 
33-630 
39-3 
•007823 
010285 
3-5564 
34-669 
49-5 
•009306 
012310 
4 - 4660 
36-281 
661 
•009819 
0 14361 
5-4784 
38-148 
85-0 
•010492 
016413 
6-6502 
40-518 
109-3 
•010968 
0-18464 
7-9247 
42-919 
135-4 
•011627 
0-20516 
9-4305 
45-967 
168-0 
•012182 
0-23593 
12-0567 
51-102 
224-5 
•013168 
0-26671 
15-1916 
56-960 
291-2 
•014284 
Using the values of temperature and emissivity given in the preceding Tables VII., 
VIII., and IX., the curves shown in fig. 11 have been drawn for the five thicker wires, 
viz., those having diameters of 14 mils, or 0 - 356 millim. ; 11T mils, or 0 - 282 millim. ; 
9'3 mils, or 0'236 millim. ; 8T mils, or 0'206 millim. ; and 6 mils, or 0T52 millim., 
respectively; and the curves shown in fig. 12 have been similarly drawn for the four 
finer wires, viz., those having diameters of 4 mils, or 0T02 millim. ; 2‘9 mils, or 
0'074 millim. ; 2 mils, or 0‘051 millim. ; and 1‘2'mil, or 0'031 millim., respectively. 
The curves for the four finest wires on fim 12 and for two of the thicker wires on 
O 
fig. 11, appear to be fairly regular throughout their whole length, while the curves 
for the 14, the 11T, and the 8'1 mils wires appear doubtful for temperatures below 
60° C. 
On examining the curves we see that:— 
1. For any given temperature the emissivity is the higher the finer the wire. 
2. For each wire the emissivity increases with the temperature, and the rate of 
increase is the greater the finer the wire. For the finest wire the rate of increase of 
emissivity with temperature is very striking. 
3. Hence the effect of surface on the total loss of heat (by radiation and convection) 
per second per square centirn. per 1° C. excess temperature increases as the tempera¬ 
ture rises. 
The wire of 4 mils diameter appears to be an exception to these rules ; but we have 
already seen reasons for believing that this wire was not drawn from pure platinum 
like the rest, but possibly from platinum-iridium or platinum-silver. 
