Ionization by Charged Particles. 811 



form of the curve was found. As before, no evidence could 

 be found of the presence of rays emerging from A with a 

 velocity greater than about 30 volts, whatever the value of 

 V x . When both V 3 and V 2 were greater than 30 volts, a 

 small positive current flowed to E, indicating the presence of 

 ■a few positively charged particles liberated within A ; but 

 the magnitude of this positive current was so small that no 

 variations of its amount could have been detected. 



In the earlier experiments it was found that the current 

 flowing to E was dependent on Y l5 even when V 2 was greater 

 than Y 1 ; it was thought that evidence had been obtained of 

 the emission o£ S rays faster than the primary. After much 

 inquiry this effect was traced to a reflexion (or emission of 

 «S rays) from the underside of Z, due to the impact of 

 electrons Jrom E which had been dragged through the 

 meshes of the gauze. When all parts o£ Z other than that 

 on which the direct light fell were covered with sealing-wax 

 and so rendered insulating, the current flowing to E was 

 entirely independent of V l5 so long as V 2 was greater than V 2 . 

 There is, again, no evidence that the 8 rays can be faster than 

 the primary. 



8. Similar experiments were made when the interior of A 

 was covered with soot. v. Baeyer and Gehrts found that 

 :such a covering diminished very greatly the reflexion of 

 electrons, but did not diminish to the same extent the emission 

 of B rays. An accurate comparison of the results with those 

 obtained when there was no soot was difficult, but it appeared 

 that the maximum number of electrons emerging from A was 

 not decreased very greatly by the presence of the soot. This 

 observation is not necessarily inconsistent with that of 

 v. Baeyer and Gehrts, for even when the interior of A is 

 polished a very small proportion of the electrons leaving Z 

 emerge from A ; the proportion emerging must be determined 

 by the geometrical form of A and by the field between A and 

 .Z rather than by the reflecting power of the walls of A. 



It appeared that the maximum number of electrons emerged 

 from the sooted box when V x is only 2 in place of 6 for the 

 polished box. On the other hand, the average velocity of 

 rthe rays emerging from A for a given value of Y x was certainly 

 greater if A is sooted ; in fact, when Y x = 40 no rays could 

 'be found emerging with a velocity less than 2 volts. 



9. The only theory of ionization which has been put 

 "forward in so definite a form that it can be made a basis for 

 the discussion of these results is that of J. J. Thomson (13). 

 Ionization is supposed to represent another aspect of the 



