of Instability of Electrified Drops, ete. 83 
The condition for instability also sets a limit to the possible 
size of charged rain drops, but the charge on drops of the usual 
size would have to be very large indeed before instability would 
arise from this cause. 
Summary. 
23. Certain motions of agitation, which are observed at the 
surfaces of drops of liquid when an electric current starts to flow 
from them, are described and the conditions under which the 
movements occur are studied (§§ 2—9). 
It is shown that in some cases (§ 10) the observed current is 
all carried by minute charged drops, formed of liquid which has 
been pulled from the discharging surface. 
The ejection of these masses from the surface occurs when the 
stabilizing effect of surface tension is overcome by the instability 
caused by the electric forces (§ 11). 
| A relation between the an at which instability begins, 
and the dimensions of the drop and the surface tension of the 
liquid, is derived for some ideal cases (§§ 11—14), and a formula 
| _ applicable to the drops used in the experiments is given (§ 15). 
In agreement with theory, the experiments show that the 
square of the potential at which instability begins is proportional 
to the surface tension of the liquid (§ 16) and to the radius of the 
tube on which the drop is formed (§ 17). 
| In air at atmospheric pressure, instability sets in before the 
true electric discharge through the gas begins, for all liquids 
except mercury (room temperature assumed) (§ 18). 
In a gas like hydrogen or in air at reduced pressures, the 
electric discharge may be obtained in many cases before insta- 
bility occurs (§ 18). 
An explanation of the observed effects is given (§§ 19, 20), and 
some outside applications of the results obtained are considered 
| (S§ 21, 22). 
A part of the work on this investigation was done at the 
Cavendish Laboratory, and I wish to express here my thanks to 
Prof. Sir J. J. Thomson for his kind and helpful interest in the 
work and for placing the necessary apparatus at my disposal. 
