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PHYSICS: R.A.MILLIKAN 
QUANTUM RELATIONS IN PHOTO-ELECTRIC PHENOMENA 
By R. A. Millikan 
RYERSON PHYSICAL LABORATORY. UNIVERSITY OF CHICAGO 
Received by the Academy, December 21, 1915 
For the past ten years I have been engaged with experiments which 
were designed for the sake of subjecting Einstein's photo-electric quan- 
tum-theory equation to searching experimental tests, and although I 
have at times thought that I had evidence which was irreconcilable 
with that equation, the longer I have worked and the more completely 
I have ehminated sources of error the better has the equation been 
found to predict the observed results. I shall present herewith the 
barest sketch of six consequences of that equation and their experimental 
verification. Preliminary reports on some of these results have already 
been made^ and detailed reports will be found in forthcoming num- 
bers of the Physical Review. 
Einstein's equation^ grew out of a semi-corpuscular quantum theory 
of radiation. The assumption was that light consists of bundles or 
'quanta' of electromagnetic energy which shoot out explosively from 
the emitting body and travel through space as localized units until they 
are suddenly absorbed by the atoms of matter upon which they fall. 
The energy in each light-unit was assumed equal to hv, in which h is 
Planck's ^wirkungs-quantum' and v is the frequency of the oscillator 
which emits the light. Upon absorption this energy was assumed to 
be transformed into the kinetic energy of an escaping negative electron 
whose energy of escape from a metal illuminated by light of frequency 
V was thus given by ^mv"^ = hv — p, in which p was the work necessary 
to separate the electron from the surface of the metal. The maximum 
energy of escape is measured by {VQ-\-K)e in which e is the electronic 
charge, K the contract EMF between the emitting plate and the op- 
posed Faraday cyhnder which catches the electron, and Fo the poten- 
tial difference which must be externally applied just to stop the photo- 
current to this cylinder. The assertions contained in the equation 
^mv^ = hv — p are that: 
1. There is a definite maximum energy of electronic emission under 
the stimulation of a given frequency v. (This has recently been denied 
by Ramsauer.^) 
2. There is a linear relation between Fo and v. 
3. The slope of the Vqv line multipKed by e is exactly Planck's *h.' 
4. The intercept of this Fo v line on the v axis is the frequency v at 
which the illuminated substance first becomes photo-sensitive. 
