THERMAL EMISSIVITY OF THIN WIRES IN AIR. 
379 
The next piece of wire used was of the same diameter, and was also a bit of the 
actual wire that had been used in the emissivity experiments. The length of this 
piece was, however, accurately known. 
Table II.—-Piece of Platinum Wire that had been used in the Experiments on 
Emissivity. 
May 14th and 15th, 1888. Diameter 14 mils, or 0'356 millim. Length 22’76 
centims. Curve No. 1, fig. 7 (Plate 11.) 
Temperature. 
Resistance, 
in ohms. 
Temperature. 
Resistance, 
in ohms. 
Temperature. 
Resistance, 
in ohms. 
0 C. 
3 C. 
° C. 
15-8 
0-262 
145-1 
0-372 
242-6 
0-452 
16T 
0-262 
145-1 
0-372 
255-2 
0-462 
52-3 
0-294 
157-3 
0-382 
256-9 
0-462 
55-0 
0-296 
168-8 
0-392 
270 1 
0-472 
63 1 
0-303 
171-6 
0-394 
271-1 
0-472 
74-5 
0-313 
180-4 
0-402 
277-8 
0-477 
85-8 
0-323 
193-1 
0-412 
278-8 
0-478 
97-5 
0-333 
206-1 
0-422 
284-6 
0-482 
0-343 
207-3 
0-422 
291-0 
0-487 
0 343 
218-6 
0-432 
298-5 
0-492 
121-4 
0-352 
230-3 
0-442 
306-1 
0-497 
132-9 
0-362 
231-9 
0-442 
The equation connecting the resistance and the temperature of the preceding 
specimens was determined in two distinct ways. First, a carve (No. 1, fig. 7) was 
drawn connecting all the values of temperature and resistance obtained on May 14th 
and 15th, then three points on this curve were selected, viz., those corresponding with 
Temperature. Resistance. 
15°-0 C. 0-262 
153°-3 C. 0-380 
300°-0 C. 0-493 
From these, on the assumption that r, the resistance at temperature t° C., could be 
expressed in terms of r 0 , the resistance at the temperature 0° C. by the equation 
r = r 0 (1 -f- at + fit 2 ) 
the values ot r Q , a, and fi were calculated. The values thus obtained were 
r 0 = 0"2487 ohm' 
a — 0 00358 ,, >-.(1). 
fi = — O'OOOOOOIOI „ J 
3 c 2 
