384 Prof. C. A. Schott: Kinetics of a System of 
were made with a sample of “emanating substance” of 
activity about 300 times uranium, obtained by Prof. Ruther- 
ford trom Dr. Giesel. The rate of decay of its emanation 
and excited activity leave little doubt that it contains the 
same radioactive constituent as the actinium of Debierne. 
The excited activity obtained from any of these three 
substances may be almost completely removed by placing 
the temporarily radioactive body in boiling dilute hydro- 
chloric acid. ‘The activity is not destroyed but remains in 
solution, and part of it may be recovered by electrolysing 
the active solution between platinum electrodes*. The 
activity thus recovered appears chiefly on the cathode, and, 
in the case of thorium, the decay of the radiation from a 
cathode thus made active is very capricious, varying from a 
decrease to half value in eleven hours to half value in two or 
three hours. When, however, a solution containing the 
activity dissolved off a platinum plate made active by ex- 
posure to the actinium emanation is electrolysed, the activity 
thus concentrated on the. cathode has a fairly constant rate 
of decay, falling to half value in about a minute and 
a half. The amount of excited activity thus recovered is 
always a very small proportion of the whole activity which 
is in solution in the acid. 
I am indebted to Prof. J. J. Thomson for his kind interest 
and assistance in a portion of the work done in the Cavendish 
Laboratory, and to Prof. Rutherford for his direction 
throughout the whole course of the investigation. 
XXXVI. On the Kinetics of a System of Particles 
illustrating the Line and Band Spectrum. 
To the Editors of the Philosophical Magazine. 
University College of Wales, 
Aberystwyth, 
GENTLEMEN,— May 11th, 1904. 
i. your issue of May there appears an article by Prof. 
Nagaoka, of Tokyo University, “On the Kinetics of a 
System of Particles illustrating the Line and the Band Spec- 
trum,” in which he considers the stability and oscillations 
of a ring of negative electrons revolving in a circle about 
a positive charge at the centre. In a letter to ‘ Nature’ of 
March 10 I pointed out that such a system is essentially 
* Von Lerch, Annalen der Physik, Nov. 1908, p. 745. 
