1909-10.] Observations on some Spark-Gap Phenomena. 229 
serious consideration. For this reason only a few phenomena, substantiated 
beyond reasonable doubt, have been quoted. These should be sufficient, 
nevertheless, to draw attention to the complete absence of a theory regard- 
ing the presence of dielectrics in a spark-gap, which will deal satisfactorily 
with all cases. The further surprising divergences met with when the 
dielectric has imposed upon it a drop or drops, of various shapes and sizes, 
of wax, stearine, etc. (see the various papers quoted — von Waltenhofen, 
Wiedemann Annalen, Bd. viii. p. 460, etc.), make the problem still more diffi- 
cult. Kiessling and Walter ( loc . cit.), in considering the bright “ threads ” of 
the brush discharge, especially when these are crowded together into one 
bright line by a stearine canal, as lines of ionic concentration, seem to have 
made the most important recent advance. It is obvious, however, that even 
that theory cannot be made to fit all cases — some of the experiments given 
here are cases in point. 
These observations are suggested by some researches which I have been 
carrying out in the Physical Institute of the University of Gottingen, and 
which are being prepared for publication elsewhere. My best thanks are 
due to Professor Riecke for suggesting the line of research, and for the 
interest he has taken in the progress of the work. 
(Issued separately February 2 , 1910 .) 
