306 BELL SYSTEM TECHNICAL JOURNAL 



plicity. Multiply now each member of the formula by h, that same 

 constant /: which we ha\e encountered three times in the course of 

 this article; and rc\erse the signs of the terms.'" The formula becomes 



hv = {-h R/n-)-{-h R'm-') (7) 



In the left-hand member there stands hv. The reader will have 

 become more or less accustomed to the notion that, under certain 

 conditions and circumstances of Nature, radiant energy of the fre- 

 quency V apparently goes about in packets or corpuscles of the amount 

 hv; now and then, here and there, energy is absorbed from such radia- 

 tion in such amounts, or energy is converted into such radiation in 

 such amounts. Suppose that this also happens when a hydrogen atom 

 radiates, whate\er the cause which sets it to radiating. Then the 

 left-hand member of the equation (5) represents the energy which 

 the hydrogen atom radiates; so also does the right-hand member; but 

 the right-hand member is obviously the difference between two 

 terms; these terms are respectively the energy of the atom before it begins 

 to radiate, and the energy oj the atom after it ceases J rom radiating. 



The problem of the hydrogen atom has now experienced a funda- 

 mental change. The proposal to make a mechanical framework, 

 having the natural vibration-frequencies expressed by (6), has been 

 laid aside. The new problem, or the new formulation of the old prob- 

 lem, is this: how can a model for a hydrogen atom be constructed, 

 which shall be able to abide only in certain peculiar and distinctive 

 states or shapes or configurations, in w'hich various states the energy 

 of the atom shall have the xarious \alues —hR, —hR 4, —hR it, 



— hR/\ii, and so forth? 



Bohr's own model has become one of the best-known and most- 

 taught conceptions of the whole science of ph>sics, in the twelve 

 years of its public existence. He based it upon the conception, then 

 rapidh- gaining ground and now generally accepted, that the hydrogen 

 atom is a microcosmic sun-and-planet system, a single electron revolv- 

 ing around a much more massive nucleus bearing an electric charge 

 ec|ual in magnitude and opposite in sign to its own. This is really 

 a most unpromising conception, very ill adapted to the modification 

 we need to make. We want an atom w^hich shall be able to assume 

 only those definite values of energy which were listed above: —hR, 



— hR A, —hR !) and the rest. Now the energy of this sun-and- 

 planet atom depends on the orbit which the electron is describing. 



'"For tlif explanation of this rather confusing reversal, see my third article (page 

 278; or page 11 of the reprint). 



