32 



Similar experiments were next performed upon ethyl- 

 chloride. The experimental results are shown on the dotted 

 diagram by (o) ; again it is seen that ordinary recombination 

 accounts for the results. 



By a separate set of experiments, as previously de- 

 scribed, it was found that between the values of field strength 

 390 and 80 volts per cm. a rise of 9 peir cent, was to be 

 expected from the pendulum experiments in the case of ethyl- 

 chloride, if the effects of initial recombination had been pre- 

 sent. This, again, was of such a magnitude that it should 

 have been readily detected. 



In the cases, therefore, of air and ethyl-chloride, which 

 both show large effects due to initial recombination when 

 the ions are collected by a field during the action of the 

 ionizing agent, no such effect can be observed when the field 

 is applied as soon as l-20th sec. after the act of ionization 

 is performed ; the act of initial recombination being fully 

 completed within this period. 



§5. 



Having now shown that effects of initial recombination 

 do not last an appreciable time, it seemed possible, by 

 means of the apparatus described in fig. 4, to obtain an in- 

 dependent verification of the theory of initial recombination. 

 For since the arrangement of the gauze in that apparatus 

 made it possible to obtain a measure of the number of ions 

 which reach the lower gauze in any given time, it was to 

 be expected, if the ionizing agent were placed, first, above 

 the lower gauze, and directly in the ionization chamber; and, 

 secondly, just below that gauze, with a current of gas 

 carrying the ions into the chamber ; that, after making proper 

 allowances for the effect of ordinary recombination in the 

 latter case, the current obtained in the first case should be 

 much greater than in the second. 



For the purpose of obtaining a steady draught, and at 

 the same time to work under any pressure with different 

 gases, the ajDparatus of fig. 4 was slightly modified. The 

 tubes were placed horizontally, and the gas was circulated 

 by means of a piston moving in a long cylinder, the ends of 

 which communicated to corresponding tubes leading from the 

 ionization chamber. The piston could be moved at a very 

 uniform speed by means of a suitably geared electro-motor. 

 The ionizing agent consisted of a small quantity of radium, 

 enclosed in a lead cell. A V-shaped slit 12 cm. deep, with paral- 

 lel faces '75 mm. apart, restricted the a rays to a fan-shaped 

 space on emerging from the cell. The cell was placed so that 



