﻿Emission Spectrum of Monatomic Iodine Vapour. 651 



which particular names might be given. In the first place, 

 there is a very thin layer close to any surface in which there 

 may be a special value for the mean concentration. This is 

 the layer discussed by Willard Gibbs, and has been called 

 after him. Its thickness is of the order of the range of 



Fig. 4. 



135 



115 

 130 



210°° ,95 



200 



205^ 



I 



1 



i 



intermolecular forces. (Secondly, there is the layer studied by 

 Perrin, " inf erieure au dixieme de millimetre," in which the 

 change of concentration of a suspensoid can be calculated 

 from an application of the laws of gases in an analogous way 

 to that in which the change of pressure of an atmosphere is 

 calculated. This is the Perrin layer. Thirdly, there is a 

 layer of one or two millimetres' thickness (in the particular 

 cases studied in this paper), in which a further change of 

 concentration occurs which cannot be calculated in the way 

 adopted by Perrin. This gradually merges into the main 

 body of the suspension, throughout which the concentration is. 

 sensibly uniform. 



LVII. On the Emission Spectrum of Monatomic Iodine Vapour. 

 By St. Lakdatj-Ziemecki, M.Sc, Lecturer in Physics, 

 High School of Agricidture, Warsaw *. 



I. The aim of this work. 



MANY of the phenomena of the multiple spectra were 

 ascribed to the dissociation of the molecules or even 

 of the atoms (the work of Lockyer may be only mentioned), 

 but there does not seem to be direct experimental evidence 

 for such a theory. On the other hand, the models of atoms 

 and molecules, now generally adopted, lead us to the idea 

 that an atom should give a spectrum quite different from the 



* Communicated by the Author. 



Presented to the Polish Academy of Sciences by Prof. L. Natanson, 

 March 7th, 1921, and published in the Bulletin de I' 'AcadSmie Polonaise, 

 serie A, 1921. Since that time the experiments have been verified by 

 the Author. 



