﻿Electricity in Flames containing Metallic Vapours. 869 



different heights. When the strip was below or on a level 

 with the bead o£ salt a small deflexion corresponding to 

 positive carriers arriving on the strip was observed on the 

 introduction of the bead, but for a certain portion above the 

 bead this metallic current increased very rapidly with the 

 height o£ the strip, and then remained approximately constant 

 until the strip was in the neighbourhood of the top o£ the 

 flame, when it again decreased. Typical distribution curves 

 are shown in fig. 1. The ordinates are the vertical h sight of 



Fig-. 1. 



Current — >■ 



the mid line of the strip above the centre of the bead, the 

 abscissae the metallic deflexions *. 



It seems reasonable to assume that the sudden increase of 

 current is due to the strip being brought into the paths of 

 the carriers coming from the lower part o£ the luminous 

 vapour streak. The much smaller deflexions (which are, 

 however, always present) for positions of the strip below 

 this are then to be ascribed to positive carriers which have 

 diffused down from the bead against the flame velocity. To 

 test this point a screen, consisting of a very carefully insulated 

 rectangle of thin platinum foil, was brought into the flame 

 between the bead and the earthed electrode, so as to cut off 

 the carriers below a certain point. The level o£ the top of 

 the screen was well above the bead. The curves obtained are 



* The three typical curves given were obtained on different days, when 

 the height of the luminous streak was somewhat different. This accounts 

 for the different extents of the flat maxima. 



