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preted in different ways, but 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 em. per sec. (3 10" em.) 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. Kirchoft 
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,” 
vy [els ® Xo 
l.e. EH = CT4 or — = 4 4 whence = —or OA = constant. 
Vo [@o) (SY 
Observation shows that the color of a ‘“‘black body” is a funetion of its 
temperature; for instance at 530° C. it glows 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 
