Some Contemporary Advances in Physics— II 



By KARL K. DARROW 



Note: Dr. Darrow, the author of the following article, has made it a 

 practice to prepare abstracts and reviews of such recent researches in 

 physics as appear to him to be of special interest. The results of Dr. 

 Darrow's work have been available to the staffs of the Bell System lab- 

 oratories for some time and having been very well regarded, it is thought 

 that such a review, published from time to time in the Technical Journal, 

 might be welcomed by its readers. 



The review- cannot, of course, cover all the published results of physical 

 research. The author chooses those articles which appear significant to 

 him or instructive to his readers, without attempting to pass judgment 

 on the scientific importance of the different papers published. It is not 

 intended that the review shall always assume the Siime form; at one time 

 it may cover many articles, at another be devoted to only a few, and it 

 may occasionally treat of but a single piece of work. 



The present installment, which is Number II, is devoted very largely 

 to the subject of atomic structure. — Editor. 



WE know quite definitely that an atom consists of a massive 

 positively-charged nucleus with a certain number of electrons 

 in its vicinity; but of the arrangement of these electrons in the strict 

 geometrical sense we know very little^indeed, we do not certainly 

 know even whether they are in motion or not. Apparently there 

 are many possible arrangements for each kind of atom; one of these 

 is a permanent arrangement, in the sense that when once established 

 it is not changed so long as the atom is not disturbed from outside; 

 the others are transient. In addition to the arrangements of the 

 electrons in the neutral atom, there are the arrangements of the 

 remaining electrons when one or more of the normal quota arc lack- 

 ing. When an atom changes over from one of these arrangements 

 to another, it must take in or give out a definite quantity of energy. 

 Another way of saying this same thing is that to each distinct ar- 

 rangement of the electrons there corresponds a distinct value of 

 the energy of the atom. These values of the energy of the atom 

 are directly or indirectly measured, often with great precision; they 

 are the data of experiment. The \'ery precise statements, or at 

 all events \X'ry definite statements, which are fninuntly made about 

 the "structure" of the atom, usually refer imly lo these energs- 

 values and the relations between them. 



The simplest question that can be asked aboiii ilie arrangement of 

 the electrons is, whether they all occupy identical positions — being, 

 for example, evenly distributed o\er the surface of a sphere or the 

 circumference of a circle, with the nucleus at its centre. If this is 

 true, the same amount of energy will be requiretl to remove any 



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