I 
THE QUANTUM [i. i 
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ii 
hi 
is maintained throughout its substance and for an indefinite 
time at a constant temperature. Inside the cavity (Hohlraum) 
there will be a continuous stream of radiation m all directions. 
The problem of radiation is that of determining the way in 
Fig. I.—Energy and Wave-length of Radiation. 
Temperatures are in degrees on the absolute scale. 
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which the energy is divided between the various wave-lengths 
or frequencies which go to make up the complete continuous 
spectrum of the full or “ black body ” radiation. 
On the experimental side the problem has been solved with 
considerable accuracy by the concordant experiments of a 
of the et 
2