temperature and structure of the sun. 81 
closed by bodies of the same temperature and if these trans- 
mit no rays, then every wave within the cavity is, in its 
quality and intensity, equi- g 
valent to radiation from mo- 
an absolutely black body 
of the same temperature; 130 
it is independent of the m 
nature and size of the 
bodies and is dependent u0 
only on the temperature.” wo 
It is only a short step from 
KirchhofFs conclusion to 
our realization, although 
it was overlooked even by 
the creator of this theory. 
If you will pardon my us- 
ing a primitive example, 
the short step was : “Punch 
a hole in the closed cavity 
as Columbus did with the 
egg!” I will omit the de- 
scription of the experi- 
mental steps in the prac- 
tical realization of cavities 
of uniform temperature 
within an interval of tem- 
peratures from — 180° C. 
up to 2300° C. and will only give the results relating to the 
radiation laws. From the distribution of energy of black 
radiation in the spectrum, represented in Fig. 1, according 
to the observations of Lummer and Pringsheim (where the 
abscissa represent the wave-lengths A in ^ — 0.001 mm. and 
the ordinates the corresponding emission at the different 
absolute temperatures T) , we can deduce the following laws : 
f 
S\d\ = a r I 
n 
a) 
A maxT= b 
( 2 ) 
