64 
PROF. H. A. WILSON ON THE ELECTRICAL CONDUCTIVITY AND 
a fraction of the atoms may be moved by the field. The average velocity of all the 
atoms due to the field will be equal to fJcX, but only a few atoms may actually move. 
If this happens, the velocities of those atoms which are moved by the field will lie 
between zero and JcX. A few atoms may be ionised all the time they are in the 
electric field and these will have the maximum velocity JcX. 
If the average life of an ion is small compared with the time the molecules are 
in the electric field, then all the molecules will move with the velocity /JcX, but if 
the average life is not small compared with the time the molecules are in the field, 
then the velocities will vary between zero and JcX, but the average for all the salt 
molecules will still be equal to fJcX. 
The rest of this paper is divided into the following sections :— 
I. Motion of luminous salt vapours in flames due to an electric field. 
II. Velocity of the positive ions of salt vapours in flames. 
III. Relation between luminosity and conductivity of salt vapours in flames. 
IV. Variation of the conductivity with the concentration of the salt vapour. 
V. Relative conductivities due to salts of different metals. 
VI. Summary and conclusion. 
Part I.— Motion of Luminous Salt Vapours in Flames due to an Electric 
Field. 
Lenard # found that the luminous streak of vapour from a salt bead in a flame 
could be deflected towards the negative electrode by a horizontal electric field. This 
deflexion has since been examined by Andrade.! 
The flame itself is also attracted by the negative electrode. Andrade observed 
the deflexion of the edge of the flame nearest to the negative electrode and 
subtracted this from the deflexion of the luminous streak to get the deflexion of the 
streak relatively to the flame gases. He found the deflexion of the flame to be about 
half that of the streak. I have repeated these experiments and found it difficult to 
be sure that there was any real difference between the deflexion of the flame and 
that of the streak of salt vapour. The edge of the flame is not sharply defined, and 
when salt was put in it seemed to me to change the deflexion of the edge of the 
flame if the vapour extended to the edge. I also found that in a flame which was 
little if at all deflected, there was little, if any, deflexion of the salt vapour, although 
a strong electric field was used. 
These preliminary experiments suggested that the deflexion of the luminous streak 
of salt vapour might be due to the deflexion of the flame as a whole, and not to a 
relative motion of the luminous salt molecules, through the flame, due to the electric 
field. 
* ‘Ann. d. Physik,’ 9, 3, pp. 642-650, Oct., 1902. 
t ‘ Phil. Mag.,’ June, 1912, and July, 1912. 
