88 
LUMMER. 
T 
Using the well-known relation w = w 0 — — , where w is the re- 
273 
sistance of a pure metal at T° absolute and w 0 the resistance at 
0° C, we get: 
Emax = C x 1 .334 x 10 i /jjT 7 16 
r .&<». = 
«/o 
— 20 
CX 4.936X10 Viv 0 T b 
Is it not astonishing that, in spite of all the limiting 
hypotheses introduced into this calculation, we get exactly 
our observed results? From this agreement we may conclude 
that these limiting hypotheses arc valid within an even 
greater range than had been supposed, and, on the other 
hand, that Lummer and Pringsheim have observed the true 
radiation laws of pure bright platinum. This was not easy 
to do, as you will see, when I tell you that Paschen found 
the total radiation of pure platinum to bo proportional to 
the 5.432 power of the absolute temperature, believing that 
this power was correct to the third decimal place. 
Using the observed relation KmxT = 2630 and assuming the 
solar radiation to be platinum radiation, the sun’s temperature 
would be 
9 a an 
Tsun = ^ = 5 260° Aba. 
0.5 
Thus we can fix the temperature of all radiating sub- 
stances whose radiation is intermediate between that of a 
black body and platinum within the two limits: 
T 
max 
Finin — 
2040 
A-tnax 
2630 
A-max 
With the aid of this hypothesis Lummer and Pringsheim 
determined the temperature of the following light sources: 
