﻿588 
  Prof. 
  Pollock 
  and 
  Mr. 
  Vonwiller 
  : 
  Experiments 
  

  

  Across 
  these 
  wires 
  is 
  placed 
  a 
  light 
  wood 
  slider, 
  the 
  wires 
  

   c 
  c 
  passing 
  through 
  small 
  glass 
  tubes 
  attached 
  to 
  it. 
  The 
  

   slider 
  carries 
  a 
  small 
  piece 
  o£ 
  hard 
  rubber 
  provided 
  with 
  two 
  

   mercury 
  cups. 
  From 
  each 
  mercury 
  cup 
  runs 
  a 
  short 
  piece 
  

   of 
  wire, 
  which 
  ends 
  in 
  a 
  single 
  loop 
  encircling 
  the 
  glass 
  tube 
  

   at 
  the 
  end 
  of 
  the 
  slider. 
  

  

  The 
  magnetic 
  detector 
  invented 
  by 
  Rutherford, 
  and 
  de- 
  

   scribed 
  by 
  him 
  (Phil. 
  Trans, 
  clxxxix. 
  (1897) 
  p. 
  8), 
  is 
  used 
  to 
  

   determine 
  the 
  characteristics 
  of 
  the 
  waves 
  along 
  the 
  wires, 
  

   the 
  ends 
  of 
  the 
  little 
  solenoid 
  of 
  the 
  detector 
  being 
  attached 
  

   to 
  the 
  mercury 
  cups 
  of 
  the 
  slider. 
  The 
  slider 
  is 
  in 
  fact 
  similar 
  

   to 
  that 
  used 
  by 
  Rubens 
  (Wied. 
  Ann. 
  xlii. 
  p. 
  154, 
  1891), 
  

   Rutherford's 
  detector 
  being 
  used 
  instead 
  of 
  the 
  bolometer-wire. 
  

   In 
  some 
  cases, 
  observations 
  have 
  been 
  taken 
  with 
  the 
  slider 
  in 
  

   various 
  positions 
  along 
  the 
  wires 
  ; 
  in 
  others, 
  the 
  slider 
  was 
  

   kept 
  near 
  the 
  ends 
  of 
  the 
  wires, 
  and 
  a 
  wire 
  bridge 
  of 
  negligible 
  

   resistance 
  placed 
  across 
  them 
  at 
  various 
  points 
  along 
  their 
  

   length. 
  In 
  both 
  cases 
  the 
  steel 
  wires 
  of 
  the 
  detector 
  are 
  

   magnetized 
  to 
  saturation, 
  the 
  detector 
  then 
  placed 
  in 
  an 
  in- 
  

   variable 
  position 
  behind 
  a 
  reflecting 
  magnetometer, 
  and 
  the 
  

   reading 
  taken. 
  The 
  solenoid 
  of 
  the 
  detector 
  is 
  then 
  attached 
  

   to 
  the 
  slider 
  wires, 
  the 
  condenser 
  discharged 
  once, 
  and 
  the 
  

   reading 
  of 
  the 
  magnetometer 
  again 
  taken. 
  The 
  difference 
  

   between 
  these 
  readings 
  is 
  in 
  all 
  cases 
  called 
  the 
  deflexion. 
  

  

  Calculation 
  of 
  the 
  Constants 
  of 
  the 
  Condenser 
  Circuit, 
  

  

  In 
  the 
  following 
  discussion, 
  the 
  wave-length 
  in 
  air 
  of 
  the 
  

   condenser 
  radiation 
  is 
  required 
  ; 
  it 
  is 
  therefore 
  necessary 
  to 
  

   calculate 
  the 
  capacity 
  and 
  inductance 
  of 
  the 
  circuit. 
  The 
  

   capacity 
  was 
  measured 
  by 
  the 
  tuning-fork 
  method, 
  that 
  of 
  

   the 
  tuning-fork 
  apparatus 
  and 
  connexions 
  being 
  carefully 
  

   eliminated. 
  

  

  The 
  results 
  of 
  these 
  experiments 
  show 
  that 
  the 
  capacity 
  of 
  

   the 
  condenser-plates 
  alone, 
  in 
  air, 
  when 
  separated 
  by 
  1*837 
  cms. 
  

   is 
  42*4 
  electrostatic 
  units. 
  The 
  discharge 
  wires 
  and 
  knobs 
  

   add 
  3'1 
  units. 
  The 
  plates 
  b 
  b 
  add 
  nothing 
  to 
  the 
  capacity. 
  

   When 
  these 
  small 
  plates 
  were 
  attached 
  to 
  the 
  wires 
  c 
  c, 
  the 
  

   measurements 
  being 
  made 
  with 
  the 
  apparatus 
  in 
  situ, 
  the 
  

   measured 
  capacity 
  was 
  increased 
  by 
  5 
  to 
  7 
  units, 
  according 
  

   to 
  the 
  length 
  of 
  the 
  wires. 
  It 
  is 
  doubtful 
  if 
  this 
  wire 
  capacity 
  

   affects 
  the 
  period 
  of 
  the 
  condenser 
  oscillation, 
  and 
  it 
  has 
  been 
  

   left 
  out 
  of 
  account. 
  The 
  capacity 
  of 
  the 
  condenser-plates 
  

   alone, 
  as 
  calculated 
  by 
  KirchhofFs 
  formula 
  (Abhandl. 
  p. 
  113), 
  

   is 
  30'62-f-9-48 
  (edge 
  correction) 
  = 
  40'10. 
  The 
  difference 
  

   between 
  this 
  value 
  and 
  that 
  found 
  experimentally 
  (42*4) 
  is 
  

  

  