SOMF. COXTF.MI'ON.IKV .IPr.lWI.S l\ /7/J'.S7( V IS W.i 



riic first tlirt'o i)f these deniancls are of a nerural and fimdamental 

 nature. If someone were to design an atotn-ni(i<iel for these phe- 

 nomena of the Stationary States and these alone, l>e would probably 

 bejjin by imaginini; an atom which would satisfy these general de- 

 mands; then he would proceed so to specialize it that it woulfl comply 

 also with the fourth. It mij^iht have been well, had this happeiv.-d; 

 the course of histor%' was otherwise. The atom-model of Rutherford 

 was desii;ned originally to interpret phenomena of fjuite another field, 

 and then Bohr modified it by violence to satisfy the fourth of the fore- 

 going demands. 



Of the facts which Rutherford ile\ised iiis atom-model to interpret, 

 the cardinal one is that the atom contains electrons. The best evi- 

 dence for this fact is, that electrons can be extracted from atoms.- 

 One can even measure the amount of energy required to extract an 

 electron from an atom — in other words, the difference between the 

 energy- of an atom in its normal state, and the energy of the same atom 

 in its "ionized" state.' This has a direct bearing on the phenomena 

 of the Stationary States; for the spectrum-terms, when they are 

 multiplied by F'lanck's constant /;, yield the energ>-values of the 

 corresponding Stationary States, reckoned from the energy-value of 

 the ionized state as zero of energy. 



Granted that the atom contains electrons: it must contain positi\e 

 electricity also, to compensate their negative charge. Now it is 

 easy to imagine the positive electricity so arranged, that the electrons 

 can be fitted into various places within and around it, and remain in 

 equilibrium*; it is possible to imagine that the positi\-e ele:"tricity acts 

 upon the electrons with a force which is compounded of the familiar 

 inverse-square attraction and a particular sort of a repulsion, so 

 adjusted that the electrons will remain in equilibrium in various 

 positions. It seems as though the Stationary States might be in- 

 terpreted in this fashion, and several attempts have in fact been 

 mafle; but they are discouraged by the experiments of Rutherford 

 and his followers on the deflections of alpha-particles and electrons 

 which pass through atoms. F"or these deflections occur exactly as if the 

 positive electricity were concentrated at a point or "nucleus," and an 

 inverse-square electric field pre\ailed in the region between this nucleus 



' This Is not quite a proof of the fact. .As .-Vston cleverly remarked, when a pistol 

 is (ircd, smoke and a bullet come out of it; we are <|uite justified in Inferring that the 

 bullet was originally within the pistol, but not the smoke! 



' This energy, which I called the energy of the "state of the Ionized atom" in the 

 First Part, Is truly the energy of the system conif csed of the atom minus its electron, 

 an<l the free electron. 



' .Although not in stable equilibrium. 



