﻿Low- Speed Positive H-Jons in Hydrogen. 810' 



The different currents in the apparatus were measured as 

 follows : — 



(a) The filament was heated by an insulated 8-volt battery 

 with resistances. The current which was usually about 

 3'5 amps, was measured by an ammeter. 



(I>) The thermionic current between F and A, which was 

 always of the order of a few milliamps., was measured by a 

 Paul single-pivot galvanometer with shunt. The constancy 

 of this current rather than its absolute value was the reason 

 for measuring it. If this current had a constant value, it 

 indicated a constancy of conditions (pressure of gas and 

 filament temperature) in the apparatus. V was measured 

 between the negative end of the filament and the cylinder. 

 It had a minimum value of about 16 volts in order to produce 

 a satisfactory supply of positive ions. 



(c) The positive-ion current leaving the cylinder for the 

 gauzes to produce ionization in Gr 2 E was measured by a 

 suspended magnet galvanometer, and was usually of the 

 order of a few microamps. The galvanometer was connected 

 between the cylinder A and the insulated battery giving x- 

 and ?/, and thus mea-ured the total positive current leaving 

 the cylinder. To compare the amount of .ionization produced 

 by a stream of positive ions accelerated through different 

 voltages, it was essential that this current should keep con- 

 stant. The positive ions were drawn out of the cylinder by 

 the field x, which penetrated inside the cylinder. This posi- 

 tive current varied with the original thermionic current, the 

 drawing-out P.D. as, and the pressure of the gas. 



It was found that for small values of x and large values 

 of V, especially with a heavy thermionic current, the current 

 leaving the cylinder was negative although the P.D. x 

 opposed a negative current. The filament v as screened from 

 the gauze Gi by the nickel-foil screen so that no electrons 

 accelerated by V could shoot through directly against x 

 towards the gauzes. With smaller values of V the current 

 leaving the cylinder was small but positive, and was probably 

 a mixture of positive and negative currents with a pre- 

 ponderance of the former. The effect was probably due 

 to the formation of a negative space-charge (inside the 

 cylinder A) which repels incoming electrons to the gauzes 

 and to the ordinary diffusion of electrons. It was impossible 

 to be certain that the positive-ion current did not contain 

 some negative current against the field x unless the value 

 of x was greater than V. These positive and negative 

 currents could not be measured separately. The field due 

 to the space-charge could not be greater than the field 



