660 Mr. J. A. Crowther on the Secondary 



It may thus be represented by the expression 



kpGrY, 

 where 



k is the factor depending npon the intensity o£ the primary 

 rays ; 



p is the pressure of the gas ; 



Gr is the "coefficient of secondary radiation" of the £as; 

 that is to say it is the proportion of the incident 

 primary radiation which is given out as secondary 

 rays by a given volume of gas under standard con- 

 ditions of temperature and pressure, and is the factor 

 which it is the object of these experiments to de- 

 termine ; and 



V is a factor depending solely upon the shape, size, and 

 position of the gas-chamber. 



The tertiary and other radiation from the walls of the gas- 

 chamber is equally proportional to the intensity of the primary 

 rays k, and to a constant C, depending upon the size, shape, 

 and materials of the gas-chamber. This portion may be 

 represented by the expression 



k . c. 



Finally the spontaneous ionization in the ionization- 

 chamber is independent of the primary radiation (the 

 chambers being efficiently screened from the rays of the bulb), 

 and may be represented by a constant S. 



The total ionization, and hence the total current through 

 the ionization-chamber may therefore be represented by the 

 expression : — 



Now let V 1? C l5 S l5 refer to one of the gas-chambers A t and 

 its corresponding ionization-chamber, and V 2 , C 2 , S 2 , to the 

 other, A 2 . 



To commence with let A x be filled with the standard gas 

 air, whose coefficient of secondary radiation is represented by 

 G , and A 2 with the gas under investigation, with a co- 

 efficient G. 



The two ionization-chambers are connected to the same 

 electroscope. One is charged to a high positive, the other to 

 an equally high negative, potential. The potential should be 

 sufficiently great to ensure complete saturation ; 400 volts 

 positive and negative was found amply sufficient. 



The gold leaf was insulated, and the number of divisions over 

 which the leaf moved in a definite time, usually 10 minutes, 



