THERMAL EMISSIVITY OF THIN WIRES IN AIR. 
381 
using three points on a curve which graphically- records the results of the experiments 
on temperature and resistance are accurate enough for practical purposes. The three- 
point method was, therefore, alone adopted for the remaining wires. Indeed, for the 
purpose of determining the temperatures of the wires in the emissivity experiments 
which corresponded with the various observed resistances, it was found most easy and 
most accurate to simply read off the temperature at once from the curves which 
recorded the results of the experiments made on the variation of the resistance with 
temperature for the particular wires. Specimens of such curves are seen in curves 1, 
2, 3, 4, 5, 6, figs. 7 and 8. (Plates 11 and 12.) 
We were, however, led to study the various formulae that had been published by 
different investigators on the connection between the resistance and temperature of 
different metals, and this led us to carry out a considerable amount of calculation 
which brought to light some interesting results. Since these results, however, are 
not specially connected with this present investigation on emissivity, we purpose 
presenting them in a separate communication later on. 
Table III.—Piece of the Platinum Wire that had been used for the Experiments 
on Emissivity. 
June 11th and 12th, 1888. Diameter, 1P1 mils, or 0'282 millim. Length, 
14'02 centims. Curve No. 2, fig. 7 (Plate 11) 
Temperature. 
Resistance, 
in ohms. 
Temperature. 
Resistance, 
in ohms. 
Temperature. 
Resistance, 
in ohms. 
°C. 
15-3 
0-2953 
°C. 
102-2 
0-365 
0 0 . 
214-0 
0'455 
156 
0-2959 
0-375 
225-6 
0-465 
16-3 
0-2962 
0-375 
226-8 
0-465 
31-8 
0-3096 
141-5 
0-395 
226-8 
0-465 
391 
0-3150 
164-9 
0-415 
238-8 
0-475 
394 
0-3150 
176-2 
0-425 
239-2 
0-475 
51-6 
0-325 
176-9 
0-425 
239-2 
0-475 
64-9 
0-335 
188-8 
0"435 
251-8 
0-485 
75-8 
0-345 
200-4 
0-445 
252-7 
0-485 
77-3 
0-345 
200-8 
0-445 
264-3 
0 495 
87-8 
0-355 
201-8 
0-445 
276-8 
0-505 
89-4 
0-355 
212-8 
0-455 
99-8 
0-365 
213-3 
0-455 
The following results (Table IV.) were not obtained with a piece of wire that had 
been actually employed in the emissivity experiments, but with a piece of wire cut off 
the same reel from which was taken the wire used in the emissivity experiments. 
Before, however, making the measurements given in Table IV., the piece of wire used 
was heated by a strong current, so as to be brightly luminous for 40 minutes, in order 
to bring it to the same state as that of the piece that had been used in the emissivity 
experiments. 
