December 14, 1917] 



SCIENCE 



595 



by assuming the square law. The effect of 

 diffusion at the lower velocities is well shown 

 by the way in which the observed values fall 

 below the corresponding calculated results. 

 The values used in each experiment for cal- 

 culating the recombination constant are 

 marked by an asterisk. 



In Table IV. the observed and calculated 

 values are given for X-rays as an ionizing 

 agent at a distance 27.7 cm. from the electro- 

 scope for an air current through a brass tube 

 2.95 cm. in diameter, using the arrangement 

 of Fig. 1. 



An attempt was made to see if the recom- 

 bination constant was a function of the qual- 

 ity of a given radiation. X- or 7-rays were 

 shot through the slit, first bare, then covered 

 by foils or sheets of lead. A series of decay 

 curves were thus obtained and the recombina- 

 tion constants calculated. Values were ob- 

 tained with the slit bare at the beginning and 

 end of the series to check the constancy of 

 the sensibility of the gold leaf. The slit was 

 covered at all times by a mica sheet .03 mm. 

 thick. 



TABLE V 



