﻿870 



Dr. E* N. da C. Andrade on the Carriers of 



shown in fig, 2. The level o£ the top of the screen corre- 

 sponds to the ordinate 0^ and it Will be observed that below 

 this there is no current. 



Currpht — ^ 



We make then the assumption that the height at which 

 the flat maximum begins corresponds to the point at which 

 the positive carriers from the lower part of the luminous 

 streak (or from just above the screen, when the screen is 

 used) arrive at the earthed electrode,*. Ihen the velocity 

 of migration of the carriers in the given field can be estimated 

 from the vertical height of the strip above the screen for the 

 position in which the large metallic current is first given. To 

 do this we must, however, consider the effect produced by 

 the portion of the path of the carriers lying in the hot air 

 between the flame and the earthed electrode. 



In the light of modern experiment it seems that positive 

 carriers of molecular size do not become appreciably loaded 

 with air molecules in such a case t« We have then to con- 

 sider the effect of (1) the variation of the electric field, which 

 is smaller in the flame than in the air-gap; (2) the variation 

 of temperature ; (3) the variation of the upward velocity of 

 the gases; 



* 'That there are present lesser currents between the point at which 

 the maximum begins and the level of the top of the screen is due to the 

 fact that the platiuum strip is of finite breadth (4 mm.). The maximum 

 first begins When the whole breadth of the strip is in the path of the 

 carriers. By the height of the strip above the screen is therefore meant 

 the height of the bottom of the strip above the top of the screen, 



t See e. g. P. Lenard arid C. Eamsauer, " tjber die Wirkuug sehr 

 kurzwelliges ultraviolleten Lichtes," Berichte der Ihidelberqer Acad. 

 Tart IV. (1911) page Vd. 



