876 Prof. J". S. Townsend and Mr. V. A. Bailey on 



The charges n 1? r< 2 , w 3 acquired by the three electrodes 

 were measured accurately by means of an induction balance. 

 The apparatus for measuring the charges was arranged so 

 that the potentials of the electrodes E 1? E 2 , E 3 deviated from 

 zero only by very small fractions of a volt while the charges 

 were being measured. 



The principal electrical quantities to be determined experi- 

 mentally area series of values of the ratio R=w a /(n 1 +n 3 +n 3 ), 

 i. e. of the charge* acquired by the central electrode to the 

 total charge, corresponding to different electric forces Z and 

 different pressures/) of the gas, and of the transverse magnetic 

 force which deflects the stream through a distance of 2' 5 

 millimetres. 



4. The value of the ratio R may also be found theoreti- 

 cally when the energy of agitation of the charged particles in 

 the stream is known, as in the case of ions where the energy 

 of agitation is the same as that of the molecules of the gas. 

 The calculations show that R is, in this case, a function of 

 the product N^Z/H, where N is the number of molecules per 

 cubic centimetre of a gas at 760 mm. pressure and tem- 

 perature equal to that of the gas through which the stream 

 is moving, e the charge of the ion, Z the electric force, and 

 IT atmospheric pressure. This function R=/NeZ/II is the 

 same for all gases, and is independent of the pressure of 

 the gas and of the mass associated with the charge e. 



A comparison of the values of R found experimentally 

 with the values given by the theoretical investigation gives 

 a method of determining the product ~Ne. A large number 

 of experiments have already been made to determine this 

 quantity, and the results have shown that the charge e is 

 the same as the charge of a monovalent ion in a liquid 

 electrolyte. 



Negative ions are formed when there is a small proportion 

 of water vapour present in the gas, and with the smaller 

 electric forces of the order 4 to 6 volts per centimetre the 

 value of R as found experimentally was in accordance with 

 the results indicated by the theory. 



Thus the conditions under which the charged particles in 

 the stream have an energy of agitation equal to that of the 

 molecules of the surrounding gas are easily attained and 

 recognized by the fact that R is independent of the pressure 

 of the gas. The ratio R for a stream of negative ions may 

 be found either experimentally or calculated by the theory 

 of diffusion, and these values of R in terms of Z may be 

 represented by means of a curve. This curve (shown in 



