458 BELL SYSTEM TECHNICAL JOURNAL 



the field, and the field-gradient, the ni;i^;iHiii' munu'iu of tlu' atom 

 can be computed very simpK . Tlu- \.iliu> tlui> (ilnaiiK-d are of the 

 order of 10 ""in CGS units. 



I shall comment in the second part of this article uyum other infer- 

 ences frf)m these experiments, which are as valuable as the experiments 

 upon the transfer of energy from electrons to atoms. At this point it is 

 sufficient lo realize that these experiments pro\e that atoms, or at least 

 the atoms of some elements, possess magnetic moment. If magnetic 

 moment is due to electric current flowing in closed orbits, as Ampere 

 and Weber guessed a century ago, the atom must be suppf)sed to 

 contain such currents; if the atom consists of a nucleus and electrons, 

 some at least among the electrons must be supposed to circulate. 

 And if the electrons are assumed to circulate in a particular manner 

 the magnetic moment of the atom so designed can be computed, 

 and thereupon tested by experiment. 



Tiiis complete^ tile list of the phentjniena, tlie jjioiierties of matter, 

 which are used in designing the contemporary atom-model. Nobody 

 will require to be con\inced that it is not a list of all properties of 

 matter, nor of all i)henomena. These are not among the obvious 

 and familiar tiualities of matter; and no one meets any of them in 

 everyday life, nor perceives an>- ol tlu'iii with his unaided senses. 

 They are phenomena of the laboralor\', discoxered after a long and 

 painstaking de\eloi)nuiit of laboratory technique. Lucretius did 

 not know tliem, and tlie.N were inaccessible even to Newton and 

 to Dal I on. Tliey are a very limited selection from among the phe- 

 nomen.i ol n.itiire, but not for that the less important. The atom- 

 model which is de\ised to explain them is at best a partial atom-model ; 

 thus far it ser\es for no other phenomena than these, but these it does 

 interpret with an elegance and a competence Cjuite without precedent 

 among atom-models. I have said that .some of these phenomena are 

 explained b>' conceiving an atom made of a positively-charged nucleus 

 and a family of electrons around it; but this conception is not tenable 

 if immodihe<l. It can be modified so as to interpret the rest of these 

 phenomena; but this means little by itself. The important fact 

 is this, that the modifications which are demanded appear in some 

 cases tf) be endf)wed with a beauty and a sim])licity, which indicate 

 that they are the expressions of an underhing principle of N.iture. 

 To these the following article will be devoted. 



