859 
therefore has been neglected by Lorentz’) and by CUNNINGHAM °*). 
Born does not separate it from the magnetization. But we can 
imagine an experiment (see below) where this effect will manifest 
itself apart from magnetism. So we shall keep these terms apart. 
Here the quadratic electric moments of the atoms appear: 
est sb, 
the same quantities which occur in recent papers of Drgijr and 
HorrsMark on the broadening of spectral lines from luminous gases 
under increased pressures.*) Half the sum of these quantities per 
unit of volume we shall call the electrical extension of matter, unless 
a better name be proposed. If an atom contains more than one 
electron, then we can have an electrical extension without polari- 
zation. We denote it by 
Kab — 1 Nest sb. 
and the corresponding part of the tensor can be written 
Owe dwt 
kab — — ZS (e) | Kee — — Ke 5 
(°) dare : Owe 
10. In order to review the results reached thus far, let us gather 
them in a scheme, and let as for convenience’ sake use rectangular 
coordinates 2, 7,2; ¢ for the time, and three-dimensional notations for 
the (three-dimensional) vectors of polarization, magnetization, and velo- 
city: p,m(m,—m”*, etc.) and w. In addition, write *K for the 
three-dimensional extension tensor, and for the new vector k: 
k= —[(K. V) wi, 
where (*K.7) is an operator having vector properties. Thus k, = 
k??, etc. Then the contents of the tensor 7’ are: 
—>b 
| em: + ke + [p.w]z -emy—ky —[p.wly pe 
zat —CiMz k, -— [p.w|- ema + Ky + [p.w |. py. 
cm, + ky, + [p.W],  -cmz — ke — [p.w]x pz 
— ps == py =p 
Applying the formula for the current from the bound electrons: 
1) Eneyelopaedie der Mathem. Wissenschaften. 
4) The Principle of Relativity, Camb. Univ. Press. 
5 P. Desye, Das molekulare elektrische Meld in Gasen, Phys. Ztschr. 20 
p. 160, 1919. 
J, Hotvsmank, Ueber die Verbreiterung von Spektrallinien, ib. p. 162, 
’ 
See also P. Desiue, Die Van ven Waausschen Kohdsionskrdfle, Phys. Zschr. 
21, p. 178, 1920. 
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