Mr Zeleny, On the Conditions, etc. 71 
On the Conditions of Instability of Electrified Drops, with 
fepereutions to the Electrical Discharge from Liquid Points. By 
JOHN ZELENY, B.A., Ph.D., Professor of Physics, University of 
Minnesota, U.S.A. (Communicated by Professor Sir J. J. Thomson.) 
: [Read 9 November 1914.] 
i\ 
_ Inarecent paper on the electrical discharge from liquid points, 
_a description is given of certain motions which are observed at the 
surfaces of such points when an electric current starts to flow from 
| them. 
_ The present paper is concerned with a study of this surface 
behaviour under a variety of conditions, and an explanation of the 
phenomena is given. 
} 
' Description of Eapervments. 
1. A discharge point of the kind in question consists of a 
‘small drop of liquid at the end of a tube, usually only a fraction 
‘of a millimetre in diameter. The drop may be made to assume 
a hemispherical form by applying a suitable pressure to the liquid 
inside of the tube. 
The arrangement of the apparatus used is shown in diagram in 
Figure 1. The discharge point A was made of glass or quartz and 
the current from it passed to the brass disc B (usually placed at a 
distance of 1°5 cms.) and then to earth through the galvanometer 
G. The reservoir C is joined to the bent glass tube D by the rubber 
tube #, which permits the reservoir to be raised or lowered for 
adjusting the pressure inside of the drop of liquid at the end of A. 
The liquid in the tubes is connected, by the wire F’, to the source 
of potential and an electrostatic voltmeter. 
In many of the experiments to be considered the essential parts 
of the apparatus were enclosed in a metal vessel to permit of work 
with various pressures and with different gases. 
Unless otherwise stated, it will be understood throughout the 
paper that a positive discharge from the point is being considered. 
2. When water is the liquid used in air at atmospheric pressure, 
it is noted, when the end of the point A is observed with a micro- 
scope, that as the potential is gradually raised, the surface of 
the drop being kept hemispherical by constant adjustment of the 
reservoir C, finally at a certain voltage the surface of the drop 
suddenly snaps back into a more flat position and the galvanometer 
indicates a momentary current. After adjusting the pressure so 
as to bring the surface to its first position, the phenomenon is only 
* J. Zeleny, Physical Review, N.S., Vol. 2, p. 69, 1914. 
