﻿574 
  Prof. 
  E. 
  H. 
  Barton 
  and 
  Mr. 
  W. 
  B. 
  Kilby 
  on 
  

  

  of 
  a 
  telescope 
  T 
  and 
  a 
  metre-scale 
  S. 
  The 
  needle 
  is 
  charged 
  

   by 
  induction 
  only, 
  and 
  therefore 
  deflects 
  in 
  the 
  same 
  direction 
  

   whatever 
  the 
  sign 
  of 
  the 
  potential 
  difference 
  under 
  exam- 
  

   ination. 
  The 
  readings 
  taken 
  are 
  those 
  of 
  the 
  first 
  throws, 
  

   which 
  are 
  sensibly 
  proportional 
  to 
  the 
  time-integral 
  of 
  the 
  

   square 
  of 
  the 
  potential 
  difference 
  of 
  the 
  disks. 
  

  

  Now 
  the 
  capacity 
  of 
  the 
  zinc-plate 
  condenser 
  is 
  of 
  the 
  

   order 
  fifteen 
  times 
  that 
  of 
  the 
  portion 
  of 
  the 
  cymometer 
  in 
  

   use. 
  Consequently, 
  if 
  we 
  maintain 
  constant 
  the 
  frequency 
  

   of 
  the 
  primary 
  oscillations 
  which 
  force 
  the 
  responding 
  circuit, 
  

   then 
  for 
  the 
  best 
  response 
  a 
  given 
  fractional 
  decrease 
  in 
  the 
  

   capacity 
  of 
  the 
  zinc-plate 
  condenser 
  will 
  involve 
  a 
  fractional 
  

   increase 
  in 
  the 
  cymometer 
  capacity 
  of 
  nearly 
  fifteen 
  times 
  

   this 
  amount. 
  In 
  making 
  observations 
  the 
  region 
  where 
  

   resonance 
  occurs 
  on 
  the 
  cymometer 
  was 
  first 
  determined 
  by 
  

   means 
  of 
  a 
  hydrogen 
  tube. 
  This 
  was 
  then 
  removed 
  and 
  

   electrometer 
  throws 
  were 
  taken 
  at 
  half-centimetre 
  steps 
  over 
  

   a 
  range 
  of 
  2 
  cm. 
  The 
  main 
  peak 
  of 
  the 
  resonance 
  curve 
  

   comes 
  well 
  within 
  these 
  limits, 
  and 
  is 
  found 
  to 
  be 
  of 
  con- 
  

   siderable 
  sharpness. 
  Further, 
  readings 
  were 
  taken 
  in 
  the 
  

   reverse 
  direction, 
  and 
  from 
  the 
  two 
  resonance 
  curves 
  thus 
  

  

  Fig. 
  5. 
  — 
  Resonance 
  Peak 
  from 
  Two 
  Curves. 
  

  

  320 
  

  

  300 
  

  

  280 
  

  

  £260 
  

   ^40 
  

  

  200 
  

  

  ISO 
  

  

  72 
  

  

  Cymometer 
  Scale. 
  

  

  obtained 
  the 
  position 
  for 
  best 
  response 
  is 
  determined 
  correct 
  

   to 
  1 
  mm. 
  or 
  less. 
  A 
  specimen 
  of 
  the 
  two 
  curves 
  which 
  

   determine 
  a 
  single 
  resonance 
  peak 
  is 
  shown 
  in 
  fig. 
  5. 
  A 
  

  

  