Flames  containing  Salt  Vapours  for  Alternating  Currents.    495 
It  is  clear  from  these  results  that  -; 7-  varies  nearly  as 
the  square  root  of  the  steady  current  due  to  a  small  P.D. 
(3)   The  Variation  of  the  Conductivity  with  the  Potential- 
Difference  and  Number  of  Alternations  per  Second. 
The  variation  of  the  conductivity  of  the  flame  as  measured 
by  —  —  7  ,  with  the  maximum  P.D.  applied  to  the  bridge 
arrangement,  was  effected  by  varying  the  length  of  the  spark- 
gap  in  the  primary  circuit  of  the  Tesla  coil.  The  spark 
passed  between  two  platinum  spheres  in  air  at  the  ordinary 
pressure.  The  following  table  gives  the  results  obtained 
when  spraying  a  solution  of  CsCl  containing  one  gram 
per  litre  : — 
Spark- 
length. 
P.D. 
(E.S.  Units 
d2. 
1      1 
d2    d\' 
VPJ)- 
at  gap.) 
(*)- 
0-0055  cms. 
2-60 
0-23 
4-05 
6-55 
0011      „ 
3-6 
0-42 
2-08 
3-95 
0-017      „ 
4-7 
0-43 
2-03 
4-4 
0-028      „ 
64 
0-48 
1-78 
4-5 
0-044      „ 
8-8 
0-50 
1-70 
5-0 
o-io 
16 
0-53 
1-59 
63 
0-20 
27-8 
0-60 
1-37 
72 
The  last  column  contains  the  products  of  -r  —  t  and  the 
d2     d1 
square    root    of    the    corresponding    potential-difference    as 
estimated  from  the  spark-length  in  the   primary  circuit  of 
the  Tesla  coil.     The  numbers  in  this  column  vary  between 
4  and  7,  while  the  P.D.  varies  by  a  factor  of   11.     Taking 
into  account  the  roughness  of  the  method  used  to  estimate 
the  P.D.  and  the  large  change  made  in  it,  we  may  conclude 
that  -5 j  probably  varies  approximately  inversely  as  the 
square  root  of  the  maximum  P.D.  applied. 
The  effect  of  varying  the  number  of  alternations  per  second 
was  tried  by  altering  the  capacity  in  the  primary  circuit  of 
the  Tesla  coil.  A  solution  containing  one  gram  of  (VC1 
per  litre  was  sprayed.  The  following  table  gives  the  results 
obtained  : — 
