L'SI 



preted in differenl ways, bul the consensus of opinion is to assign them to 

 one of two kinds: first, magnetic and electro-static phenomena caused 

 by strains in the ether and. second, based upon a dynamic disturbance; dis- 

 turbances which can be propagated through the ether at the rate of three 

 times ten to the tenth cm. per sec. (3 X 10 1 " cm.) These ether waves pro- 

 ceeding radially from the source carrying with them, not matter, in its 

 old sense, but energy. 



It is an established fact that all bodies emit radiant energy in some 

 degree; the intensity of this radiation being dependent upon the character 

 of the body, its surface peculiarities and upon its temperature. Kirchoff 

 gave us a law which states a relation between the emissive and absorptive 

 power of bodies, "that the ratio between the absorptive power and the 

 emissive power is the same for all bodies at the same temperature and that 

 the value of this ratio depends only on the temperature and the wave length." 

 For a "black body" this ratio is considered unity in as much as it absorbs 

 all the radiant energy which falls upon it. While we know of no substance 

 which may be considered a "black body" in this sense, the radiations within 

 a uniformly heated enclosure may be considered to approximate those ema- 

 nating from a perfectly "black body." 



Stefan's law takes us a step further and gives us a relative measure of 

 the radiation of a black body emitted at different temperature. The law 

 states that "the total energy radiated by a black body is directly proportional 

 to the fourth power of the absolute temperature of the radiating body," 



^ [ el 4 e \o 



i. e. E = CT 4 or — = -s — \ whence — = — or 6X = constant. 



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Observation shows that the color of a "black body" is a function of its 

 temperature; for instance at 530° C. it gloAvs with a dull red; at 1000° C. 

 the red gives place to a yellow and when 1200° C. to 1250° C. has been 

 reached it has grown white hot or incandescent. In the spectrum of a black 

 body we find the distribution of energy to be dependent upon its temperature. 

 Wien has shown "that as the temperature of the body rises that the peak 

 of the energy curve is displaced towards the shorter wave length." While 

 Wien's law and his proposed revision stated in his second law satisfied 

 the conditions obtaining in a limited area of the visible spectrum it was found 

 not to hold true with respect to facts relating to wave lengths lying in the 



