356 Prof. J. A. McClelland on the 
direct test of the matter, as Rutherford’s work is not con- 
clusive on this point. 
Rutherford has had emanation for long periods in closed 
vessels, and under the action of an electric field, in which 
case we should expect the emanation, if charged, to be driven 
to one or other of the terminals ; and as this does not happen, 
the indication is that it is not charged. But if the mass 
travelling with the electric charge were great in comparison 
with the charge, the motion under electric force would be 
very slow, and the emanation would not move to the terminals. 
Description of Apparatus. 
Five milligrammes of radium bromide were dissolved in 
water contained in a small vessel R covered with a slip of 
thin paper through which the emanation readily passes. The 
vessel R is placed under a large air-tight bell-jar A. A 
second large air-tight bell-jar B is joined up as shown in the 
figure. O is a vessel filled with glass-wool ; and D isa metal 
G 
hase 
4 y & DAY Y 
chi & AZZe 
ZK 
SJ 
SSS 
> 

fit 
Hi 
fii 
6 ort E 
b ae a Bs 
ARTH 
a FN 
CELLS ~“*ee-> EARTH 
cylindrical vessel resting on blocks of paraffin, and fitted 
with a paraffin stopper, in which is fixed the metal rod T. 
The glass tube F dips into mercury, and acts as a gauge to 
show the pressure when D is partially exhausted, the ex- 
haustion being produced by applying a pump at G. The 
letters t,, t., and t; denote taps by which the tubes can be 
closed at the points indicated. E isa quadrant electrometer. 
one pair of quadrants being permanently to earth, and the 
other pair joined to a mercury cup 6 ina block of paraffin. 
The cup d is kept connected to an earthed cup a, except when 
an observation is to be taken, and then the connecting piece 
