254 Mr. G. Owen on the Discharge of 
(7) Nature of the Carriers of the Electricity discharged from 
the Filament at very Low Pressures. 
eraepee on this point has been obtained by finding the 
value of < for the carriers of the electricity. The method 
adopted for this determination was that used by Prof. J. J. 
Thomson * for the ions discharged from a carbon filament. 
The principle of the method is to subject the ions to the 
joint action of electric and magnetic forces, the directions of 
the forces being at right angles to one another. It is shown 
in the paper referred to that the value of e/m is given by the 
expression 3, where d is the distance from the filament to 
2V 
Ha? 
the electrode, H the magnetic force, and V the largest 
potential-difference between the filament and electrode under 
which any diminution of the leak due to the magnetic field 
can be detected. This is obviously the same as finding the 
smallest magnetic force which produces a diminution in the 
leak under a given potential-difference V. The latter method 
was used in the experiments described in this section. 
In order to swamp the. alternations of potential on the 
filament, the latter was charged to very high voltages. The 
leak without any magnetic field was first noted. “Magnetic 
fields of various magnitudes were then put on by sending 
currents through an electromagnet, between the poles of 
which the filament was placed, and finally the leak without 
the magnetic field was once more observed. 
The results obtained on March 5th for the negative leak in 
avacuum are given in Table XIII. The filament was midw ay 
between the platinum disks which were 7 mms. apart. 
It will be noticed that weak magnetic fields increase the leak 
slightly. The same effect was noticed by Prof. J. J. Thomson 
in his experiments on the magnetic deflexion of the cor rpuscles 
from a carbon filament. Theoretically, if the carriers are 
particles of a uniform mass starting at the same distance 
from the electrodes, then a magnetic field smaller than a 
certain value will produce no diminution in the leak, while 
a magnetic field greater than this critical value will stop the 
leak entirely. This, however, is never realized in practice ; 
but the transition from no effect to a reduction of the leak 
by 80 per cent. is very fairly abrupt, as may be seen from the 
curves in diagram 9 (p. 256), which represent the results 
given in Table XIII. 
* Phil. Mag. xlvill. pp. 547-567 (1899). 
