[ 89 |] 
Wale 
ON THE EMANATION GIVEN OFF BY RADIUM. 
By J. A. McCLELLAND, M.A., 
Professor of Experimental Physics, University College, Dublin. 
[Read, January 19, 1904. } 
THE a rays of radium have been proved to consist of positively charged par- 
ticles moving with great velocity, the mass of the particle being comparable with 
that of the hydrogen atom. ‘The 6 rays have also been shown to consist of charged 
particles moving with great velocity, the charge in this case being negative, and 
the mass of the particles very small compared with that of even the hydrogen atom. 
Little is known as yet about the y rays, except that they have very great 
penetrating power. 
The emanation produced by radium has been much studied, and many of its 
properties are known; but it does not appear to have been definitely settled 
whether or not the emanation particles are charged ; and it is important to be 
certain on this point when framing a conception of the manner in which the 
radium atom disintegrates. The object in this paper is to test as accurately as 
possible whether or not the emanation carries an electric charge. Rutherford’s 
work indicates that it is not charged; but I have thought it advisable to make a 
direct test of the matter, as Rutherford’s work is not conclusive 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 are dissolved in water contained in a small 
vessel & covered with a slip of thin paper through which the emanation readily 
passes. ‘The vessel # is placed under a large air-tight bell-jar A. A second large 
air-tight bell-jar B is jomed up as shown in the figure. C is a vessel filled with 
glass wool; and D is a metal cylindrical vessel resting on blocks of paraffin, and 
fitted with a paraffin stopper, in which is fixed the metal rod 7. The glass tube 
F dips into mercury, and acts as a gauge to show the pressure when D is partially 
TRANS. ROY. DUB. SOO., N.S.» VOL. VIII, PART VI. Q 
