i of Instability of Electrified Drops, ete. 79 
results, obtained some time ago with a number of liquids, are given 
im Table I for the potentials at which the surface oscillations, 
indicative of instability, ceased as the voltage was decreased. The 
list of liquids is confined to those which have an appreciable con- 
ductivity and still do not leave a solid residue on evaporation. The 
experiments were done in the open air (pressure = 74 cms. of 
mercury) with the point at a distance of 1°5 cms. from a plate. 
TABLE I. Instability Potentials. 
Radius of point, 00250 cm. Average temperature, 23° C. 
Substance Density | Surface tension} Instability potential Cc 
PAIEOLONE! o5......: 0-790 | 24:9 dynes/cm.| 9°30 electrostatic units| 140 
Methyl alcohol | 0:804 |253 ° ,, 9-25 i 137 
| Ethyl alcohol...) 0-812 | 25:3 Hi 9°25 . 137 
Waiter ..........-. 0-998 | 72-0 ze 15:90 Sete 140 
Acetic acid...... 1:053 | 30-0 i 9°67 ss 125 
Glycerine ...... 1259 |652 ,, 15°17 ‘ 142 
Chloroform..... AC | GO 10°17 * 153 
Column 2 gives the densities of the liquids named in column 1. 
Column 3 gives the values of the surface tensions of the liquids, 
determined while in the apparatus by measuring the pressure in 
‘an uncharged hemispherical drop. These values are not very 
accurate as the readings for them were taken incidentally only, as 
_the experiments were made for another purpose for which the surface 
| tensions were not needed. ‘The value given for the surface tension 
of glycerine was taken from tables, as a difficulty was found in the 
direct measurement owing to its high viscosity ; and the value for 
methyl alcohol is taken the same as that of ethyl alcohol since no 
‘direct measurement was made and the two substances have very 
nearly the same value. 
Column 4 gives the observed instability potentials expressed in 
electrostatic units. The last column gives the values of the constant 
Cin expression (10), as calculated for each liquid from the tabulated 
values of V, a, and 7’. 
When account is taken of the rather large experimental errors 
in the determinations of 7’, the values of C are nearly enough alike ~ 
to show that the squares of the potentials at which instability begins 
are proportional to the surface tensions of the liquids. 
17. For showing the dependence of V upon the radius of the 
discharge point, reference is made to a table of electric intensities, 
J, given in a previous paper (loc. cit., p. 88) which were determined 
at the surfaces of water drops ranging in radius from 0:0146 cm. 
VOL, XVIII. PT. II. 6 
