﻿20 
  M. 
  I. 
  Pupin 
  — 
  Automatic 
  Mercury 
  Vacuum 
  Pump. 
  

  

  connection 
  is 
  to 
  keep 
  the 
  gas 
  pressure 
  above 
  and 
  below 
  the 
  

   mercury 
  in 
  the 
  reservoir 
  the 
  same. 
  Two 
  ground 
  joints 
  h 
  and 
  

   n 
  are 
  made 
  air-tight 
  by 
  the 
  mercury 
  which 
  fills 
  the 
  surround- 
  

   ing 
  hoods. 
  These 
  joints 
  connect 
  this 
  extension 
  to 
  a 
  manometer 
  

   and 
  the 
  vessel 
  F 
  which 
  is 
  to 
  be 
  exhausted. 
  

  

  3. 
  The 
  Syphon 
  barometer 
  connection. 
  

  

  This 
  is 
  the 
  part 
  consisting 
  of 
  the 
  bulb 
  c 
  and 
  the 
  tube 
  cf. 
  

   The 
  length 
  of 
  this 
  tube 
  is 
  about 
  80 
  cm 
  . 
  

   All 
  the 
  parts 
  are 
  made 
  of 
  glass. 
  

  

  The 
  modus 
  operandi. 
  

  

  First 
  a 
  little 
  mercury 
  is 
  poured 
  through 
  z 
  s 
  into 
  A 
  until 
  the 
  

   reservoir 
  c 
  is 
  about 
  half 
  full, 
  which 
  is 
  considerably 
  more 
  than 
  

   sufficient 
  to 
  fill 
  the 
  tube 
  cf. 
  By 
  means 
  of 
  a 
  rubber 
  tube, 
  z 
  s 
  is 
  

   connected 
  then 
  to 
  a 
  water-pump 
  or 
  any 
  other 
  suction 
  pump 
  that 
  

   may 
  be 
  available. 
  Suppose 
  that 
  this 
  auxiliary 
  suction 
  pump 
  is 
  

   capable 
  of 
  reducing 
  the 
  pressure 
  in 
  A 
  to 
  say 
  40 
  mm 
  and 
  suppose 
  

   also 
  that 
  the 
  barometric 
  pressure 
  is 
  760 
  mm 
  . 
  Owing 
  to 
  the 
  

   action 
  of 
  the 
  auxiliary 
  suction 
  pump 
  the 
  gas 
  pressure 
  in 
  A 
  

   is 
  continually 
  reduced 
  and 
  therefore 
  also 
  in 
  F 
  and 
  in 
  all 
  other 
  

   parts 
  connected 
  with 
  A. 
  Mercury 
  rises 
  in 
  the 
  valve 
  and 
  suction 
  

   tubes 
  and 
  also 
  in 
  the 
  tube 
  of 
  descent. 
  The 
  extremity 
  m 
  of 
  

   the 
  suction 
  tube 
  is 
  placed 
  at 
  such 
  a 
  distance 
  below 
  the 
  initial 
  

   level 
  of 
  the 
  mercury 
  in 
  E 
  and 
  D 
  that 
  when 
  the 
  mercury 
  col- 
  

   umn 
  in 
  the 
  suction 
  tube 
  is 
  about 
  60 
  cm 
  long 
  the 
  mercury 
  level 
  

   in 
  E 
  (which 
  sinks 
  rapidly 
  on 
  account 
  of 
  the 
  rising 
  of 
  the 
  mer- 
  

   cury 
  into 
  the 
  valve 
  tube) 
  has 
  just 
  reached 
  m. 
  From 
  that 
  

   moment 
  on 
  no 
  more 
  mercury 
  gets 
  into 
  the 
  suction 
  tube. 
  But 
  

   owing 
  to 
  the 
  action 
  of 
  the 
  auxiliary 
  pump 
  the 
  pressure 
  in 
  A 
  is 
  

   being 
  still 
  reduced, 
  hence 
  the 
  column 
  in 
  the 
  valve 
  tube 
  rises 
  

   still 
  higher 
  and 
  the 
  level 
  in 
  E 
  sinks 
  still 
  lower. 
  In 
  the 
  mean 
  

   time 
  the 
  column 
  in 
  the 
  suction 
  tube 
  rises 
  bodily 
  owing 
  to 
  the 
  

   external 
  air 
  pressure 
  until 
  it 
  reaches 
  the 
  narrow 
  part 
  ab 
  when 
  

   it 
  begins 
  to 
  lengthen 
  out, 
  and 
  since 
  ab 
  is 
  20 
  cm 
  long 
  and 
  the 
  

   initial 
  length 
  o 
  f 
  ' 
  the 
  mercury 
  column 
  is 
  60 
  cm 
  it 
  follows 
  that 
  

   this 
  column 
  will 
  be 
  lengthened 
  out 
  to 
  70 
  cm 
  and 
  no 
  more. 
  

   Hence 
  as 
  soon 
  as 
  the 
  pressure 
  in 
  A 
  has 
  been 
  reduced 
  by 
  TO 
  ™ 
  

   this 
  column 
  will 
  rise 
  with 
  accelerated 
  velocity 
  until 
  it 
  is 
  

   injected 
  by 
  the 
  external 
  air 
  pressure 
  into 
  the 
  reservoir 
  A. 
  The 
  

   external 
  air 
  rushes 
  then 
  into 
  A 
  and 
  through 
  tvw 
  into 
  the 
  

   valve 
  tube. 
  The 
  valve 
  tube 
  column 
  sinks 
  and 
  the 
  level 
  in 
  E 
  

   rises. 
  But 
  it 
  will 
  rise 
  more 
  rapidly 
  in 
  D 
  than 
  in 
  E 
  owing 
  to 
  

   the 
  friction 
  of 
  the 
  narrow 
  rubber 
  tube 
  connecting 
  the 
  two 
  

   vessels 
  E 
  and 
  D. 
  Hence 
  it 
  will 
  continue 
  to 
  rise 
  for 
  a 
  short 
  

   time 
  even 
  after 
  it 
  has 
  reached 
  m 
  and 
  by 
  closing 
  the 
  suction 
  

   tube 
  started 
  again 
  the 
  action 
  of 
  the 
  auxiliary 
  suction 
  pump. 
  

  

  