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are integral multiples of some fundamental unit of energy. This implies 
that energy is emitted from a body in some definite, finite unit and is closely 
related to his idea that the entropy of a body is a function of the probability 
of its present state. 
Conceiving the emission of radiant energy as explosive in type and not 
continuous, Planck concludes that these energy units may not be neces- 
sarily of the same magnitude. When a system is vibrating with high fre- 
queney, a large amount or large unit of energy is associated with it, whereas 
one of low frequency gives out smaller quantities or units of energy, thus 
giving us an explanation why so little energy is found in one end of the spec- 
trum. The fact that some bodies have low thermal capacities at low tem- 
peratures and that these increase with rise in temperature is Indicative of 
the value of this theory. In this connection it is interesting to note that 
an explanation of the hydrogen lines in the spectrum has been proposed, 
based on the idea that no radiations take place except when one electron 
vibrating changes the form of its orbit, at which instant the energy change 
of the system is the same. Take the case of the line spectra; it has been 
asserted that the lines in the spectrum of hydrogen are due to various 
electronic vibration frequencies in the hydrogen atom, when the equilibrium 
of this atom has been disturbed; but when this electron is vibrating about 
the so-called positive core of the atom that we have an entire system in 
equilibrium. As long as these vibrations are regular no energy can be sent 
forth, inasmuch as by this, the equilibrium of the system would be disturbed. 
With this disturbance there would be a change in its vibration frequency 
and assuming the radiation emission to be continuous it follows that the 
frequency change will likewise be continuous; but this at once results in the 
destruction of the lines in the spectrum. An ingenious explanation of these 
hydrogen lines has been proposed based on Planck’s Quantum theory. The 
electron is conceived of as vibrating about the central core in some form of 
a stable orbit, probably ellipical in shape. At the instant that one of these 
orbits changes form radiation will take place. At this instant the radiation 
will be of one frequeney and the energy change will be represented by EK =hn 
where n is frequency of vibrations and h is the universal constant of 
‘ 
radiation and is termed by Planck the “‘operating quantity.” 
The problem is a very complex one and has been approached from many 
angles. The Zeeman effect produced when a light and heat center is placed 
in a magnetic field offers additional evidence relative to the shifting of line 
