﻿432 
  Prof. 
  C. 
  H. 
  Lees 
  on 
  Vascliy^s 
  or 
  Pirani's 
  Method 
  

  

  accuracy 
  be 
  desired, 
  which 
  can 
  rarely 
  happen 
  owing 
  to 
  the 
  

   uncertainty 
  as 
  to 
  the 
  value 
  o£ 
  /x. 
  But 
  i£ 
  it 
  be 
  retained, 
  

   the 
  resistance 
  becomes 
  

  

  where 
  z 
  has 
  the 
  value 
  in 
  (39), 
  and 
  the 
  brackets 
  may 
  be 
  

   shortened 
  except 
  when 
  z 
  is 
  nearly 
  unity. 
  

  

  When 
  the 
  frequency 
  is 
  smaller, 
  this 
  makes 
  R 
  = 
  ^a-lira?^ 
  

   the 
  value 
  appropriate 
  to 
  steady 
  currents. 
  

  

  Copper 
  Wires 
  with 
  Low 
  Frequency. 
  

  

  The 
  formula 
  suited 
  to 
  this 
  case 
  is, 
  writing 
  /S^ 
  + 
  y^ 
  z= 
  a, 
  if 
  

   (zu^fy) 
  are 
  defined 
  as 
  in 
  (39), 
  and 
  under 
  the 
  same 
  

   limitations, 
  

  

  ZT? 
  <v 
  A-nn 
  

  

  ^ 
  =T 
  • 
  a 
  - 
  ^(^-2«P^ 
  + 
  27p^2)/(l-4^^^ 
  + 
  4a/,V) 
  

  

  Sna^ 
  

  

  log 
  ^ 
  (72-^2 
  _^^_^ 
  2cc^pz)l(l 
  - 
  4^pz 
  + 
  4ap^z') 
  , 
  (51) 
  

  

  again 
  reducing 
  to 
  2cr/7ra^ 
  for 
  steady 
  currents. 
  

  

  Trinity 
  College, 
  Cambridge, 
  

   April 
  21, 
  1909. 
  

  

  L. 
  On 
  Vaschy's 
  or 
  Pirani's 
  Method 
  of 
  comparing 
  the 
  Self- 
  

   Inductance 
  of 
  a 
  Coil 
  with 
  the 
  Capacity 
  of 
  a 
  Condenser, 
  

   By 
  Charles 
  H. 
  Lees, 
  D.Sc, 
  F.R.S., 
  Professor 
  of 
  Physics 
  

   in 
  the 
  Fast 
  London 
  College, 
  University 
  of 
  London 
  *. 
  

  

  IN 
  a 
  recent 
  number 
  of 
  U 
  Eclairage 
  Flectrique, 
  M. 
  0. 
  de 
  

   A. 
  Silva 
  t 
  examined 
  in 
  detail 
  the 
  validity 
  of 
  Vaschy's 
  or 
  

   Pirani^s 
  method 
  of 
  comparing 
  the 
  self-inductance 
  of 
  a 
  coil 
  

   with 
  the 
  capacity 
  of 
  a 
  condenser 
  for 
  the 
  case 
  in 
  which 
  the 
  

  

  * 
  Communicated 
  by 
  the 
  Author. 
  

  

  t 
  0. 
  de 
  A. 
  Silva, 
  L'Eclairage 
  Electrique, 
  50. 
  p. 
  113 
  (1907). 
  

  

  