﻿A. 
  G. 
  Webster 
  — 
  Rapid 
  Break 
  for 
  large 
  Currents. 
  383 
  

  

  Aet. 
  XXXYI. 
  — 
  A 
  Rapid 
  Break 
  for 
  large 
  Currents 
  ; 
  by 
  

   A. 
  GL 
  Webster, 
  Ph.D. 
  

  

  The 
  necessity 
  frequently 
  arises 
  of 
  breaking 
  a 
  current 
  of 
  a 
  

   number 
  of 
  amperes 
  with 
  regularity 
  and 
  considerable 
  rapidity, 
  

   particularly 
  in 
  connection 
  with 
  induction 
  coils, 
  as 
  in 
  the 
  

   experiments 
  of 
  Hertz, 
  Tesla, 
  and 
  recently 
  of 
  Roiitgen. 
  The 
  

   breaks 
  usually 
  furnished 
  with 
  induction 
  coils 
  are 
  useless 
  for 
  

   much 
  more 
  than 
  five 
  amperes, 
  and 
  are 
  at 
  best 
  slow 
  and 
  irregu- 
  

   lar. 
  Mercury 
  breaks 
  are 
  usually 
  very 
  disagreeable 
  to 
  work 
  

   with 
  and 
  soon 
  become 
  useless 
  from 
  oxidation. 
  Perhaps 
  as 
  

   simple 
  and 
  satisfactory 
  a 
  break 
  as 
  any 
  is 
  a 
  revolving 
  slate 
  disc 
  

   with 
  metallic 
  sectors, 
  as 
  used 
  by 
  Wadsworth, 
  Pupin, 
  and 
  others, 
  

   with, 
  if 
  necessary, 
  an 
  arrangement 
  for 
  blowing 
  out 
  the 
  spark. 
  

   Such 
  breaks, 
  however, 
  usually 
  burn 
  up 
  in 
  time. 
  If 
  a 
  very 
  

   regular 
  break 
  is 
  necessary, 
  however, 
  this 
  device 
  is 
  not 
  applic- 
  

   able, 
  and 
  one 
  naturally 
  has 
  recourse 
  to 
  a 
  tuning-fork. 
  Such 
  a 
  

   necessity 
  presented 
  itself 
  to 
  the 
  writer 
  when 
  he 
  attempted 
  to 
  

   regulate 
  the 
  speed 
  of 
  an 
  electric 
  motor 
  as 
  described 
  in 
  the 
  

   preceding 
  article. 
  With 
  a 
  tuning-fork 
  a 
  mercury 
  break 
  

   becomes 
  a 
  necessity, 
  as 
  anything 
  else 
  would 
  produce 
  too 
  great 
  

   a 
  disturbance 
  in 
  the 
  period 
  of 
  the 
  fork. 
  In 
  order 
  to 
  prevent 
  

   burning 
  up 
  the 
  mercury 
  the 
  contact 
  must 
  take 
  place 
  under 
  

   some 
  fluid. 
  Water 
  is 
  dirty, 
  alcohol 
  takes 
  fire, 
  and 
  other 
  liquids 
  

   generally 
  produce 
  a 
  great 
  amount 
  of 
  refuse 
  in 
  a 
  short 
  time. 
  It 
  

   is 
  therefore 
  necessary 
  to 
  keep 
  a 
  current 
  of 
  liquid 
  flowing 
  over 
  

   the 
  mercury. 
  After 
  trying 
  a 
  stream 
  of 
  water 
  for 
  some 
  time, 
  

   and 
  finding 
  that 
  the 
  mercury 
  gradually 
  disappeared 
  from 
  oxi- 
  

   dation, 
  and 
  that 
  the 
  platinum 
  wire 
  was 
  also 
  consumed, 
  the 
  

   writer 
  was 
  laying 
  the 
  matter 
  aside 
  when 
  he 
  was 
  informed 
  by 
  

   Professor 
  Wadsworth, 
  of 
  the 
  University 
  of 
  Chicago, 
  that 
  a 
  

   stream 
  of 
  mercury 
  from 
  a 
  jet 
  was 
  used 
  in 
  the 
  laboratory 
  there, 
  

   for 
  currents 
  of 
  one 
  or 
  two 
  amperes, 
  the 
  idea 
  having 
  been 
  sug- 
  

   gested, 
  I 
  believe, 
  by 
  Professor 
  Stratton 
  of 
  that 
  university. 
  A 
  

   jet 
  of 
  water 
  had 
  been 
  previously 
  used 
  by 
  Bedell 
  and 
  Crehore. 
  

   It 
  occurred 
  to 
  the 
  writer 
  that 
  if 
  the 
  break 
  were 
  made 
  under 
  

   water, 
  and 
  the 
  mercury 
  were 
  continuously 
  elevated, 
  that 
  this 
  

   would 
  furnish 
  the 
  desired 
  break. 
  

  

  The 
  first 
  thing 
  that 
  suggested 
  itself 
  as 
  a 
  means 
  of 
  elevating 
  

   the 
  mercury 
  was 
  an 
  application 
  of 
  the 
  ingenious 
  device 
  

   described 
  by 
  Dr. 
  Pupin, 
  in 
  connection 
  with 
  a 
  Sprengel 
  air- 
  

   pump 
  (this 
  Journal, 
  January, 
  1895). 
  A 
  short 
  experience 
  with 
  

   a 
  vertical 
  mercury-jet 
  surrounded 
  by 
  a 
  stream 
  of 
  water 
  showed 
  

   that 
  this 
  arrangement 
  would 
  not 
  answer, 
  on 
  account 
  of 
  spatter- 
  

   ing 
  of 
  both 
  water 
  and 
  mercury. 
  The 
  arrangement 
  finally 
  

  

  