Discontinuity in the Phenomena of Radiation 7 1 



any one of these curves takes the form which I put on the board* 



beside the original parabola. The discrepancy between theory 

 and experiment could not be more forcibly illustrated. Instead 

 of the greater part of the energy residing in vibrations of very 

 high frequency, it is largely concentrated in vibrations around a 

 certain mean frequency, this mean frequency changing to a higher 

 value, with, of course, a shorter wave-length, as the temperature 

 of the enclosure rises. To emphasise the point still further, let 

 me show you the energy curves of the radiation from the sun 

 (freed from the absorption of the solar and terrestrial atmos- 

 pheres), the electric arc, and a gas flame, all sources which 

 approximate closely to the condition of " full radiators." The 

 same type of curve with its maximum peak appears just as in the 

 previous slide. Let me also give one numerical illustration which 

 can be deduced from such curves. A mass of iron at the freezing 

 point of water is situated inside an enclosure whos^ walls are 



Fig. 5. 



