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L. Molecular Refractivity and Atomic Interaction. II. By 

 L. Silberstein, Ph. I)., Lecture?' at the University of 

 Rome *. 



IN what follows, my first paper on this subject, Phil. Mag. 

 vol. xxxiii. pp. 92-128, will be shortly referred to as I., 

 and, if not otherwise stated, all symbols will have their 

 previous meaning. 



1. Atomic Interaction ; Corrigendum, 



By an inadvertence formula (4), p. 100, I., has been 

 written for " the whole force " on the i-th electron due 

 to the j-th. atom (or ^-th doublet). That formula repre- 

 sents, obviously, that part of the force which is due to 

 the axial component alone of the displacement r.. The 

 mutual distance R of the two atomic centres being large as 

 compared with r-, the^-th atom acts as an ordinary, and 

 well familiar, doublet, and exerts on the dispersive electron 

 of the i-th atom the total force 



V.. = J*L [3u(ur,)-r-], 



where u is a unit vector drawn from the i-th to the ^-th 

 centre, or vice versa f, the charges e i9 e- being now taken 

 in rational units. In Cartesians, if f, v, fare the rectangular 

 coordinates of j, with origin in i, and r x , r ■ r z the components 

 of the displacement r ., the components of the bracketed vector 



will have the familiar form r x y '-^ — 1 \ + 3r y ^ 2 + 3r z |^ 2 , etc. 



Let us write p = <?r for the electric moment of any doublet. 

 Then the above fundamental formula will become 



F - = ^ [3u(u ^- p ^ (1) 



The axial component of this force is \ -L., -, as in I., while 



the transversal part is given, in size and direction, by the 

 vector ^[ufup) — p]/47rit 3 . The latter is, obviously, in 

 general, of the same order as the axial component and can, 



* Communicated by the Author. 



f This is immaterial, since u enters only through the dyad u . u which 

 retains its value on changing the sign of u. 



Phil. Mag. S. 6. Vol. 33. No. 198. June 1917. 2 



