﻿the 
  Condenser 
  in 
  an 
  Induction- 
  Coil. 
  453 
  

  

  Discussion. 
  

  

  The 
  curves 
  for 
  the 
  two 
  coils 
  both 
  indicate 
  that 
  for 
  a 
  given 
  

   primary 
  current 
  there 
  is 
  a 
  corresponding 
  special 
  capacity 
  

   which 
  makes 
  the 
  secondary 
  spark-length 
  a 
  maximum. 
  They 
  

   also 
  show 
  that 
  the 
  value 
  of 
  the 
  capacity 
  for 
  maximum 
  spark- 
  

   length 
  becomes 
  larger 
  as 
  tbe 
  primary 
  current 
  becomes 
  stronger. 
  

   Again, 
  the 
  character 
  of 
  the 
  curves 
  is 
  such 
  that 
  each 
  of 
  them 
  

   rises 
  very 
  rapidly 
  at 
  first 
  until 
  a 
  maximum 
  point 
  is 
  reached, 
  

   and 
  then 
  falls 
  down 
  somewhat 
  gradually. 
  

  

  Hence 
  below 
  this 
  maximum 
  point 
  the 
  effect 
  of 
  capacity 
  is 
  

   to 
  increase 
  the 
  secondary 
  spark-lengths 
  at 
  a 
  rate 
  much 
  greater 
  

   than 
  that 
  at 
  which 
  it 
  diminishes 
  them 
  beyond 
  this 
  point. 
  

   Since 
  the 
  sole 
  object 
  of 
  an 
  induction-coil 
  is 
  to 
  get 
  the 
  greatest 
  

   possible 
  spark-length, 
  that 
  is 
  to 
  say, 
  the 
  highest 
  attainable 
  

   potential-difference 
  at 
  the 
  secondary 
  terminals, 
  makers 
  of 
  

   induction-coils 
  must 
  pay 
  great 
  attention 
  to 
  the 
  above 
  fact. 
  

  

  An 
  insufficient 
  as 
  well 
  as 
  an 
  excessive 
  capacity 
  spoils 
  the 
  

   action 
  of 
  coils 
  to 
  a 
  large 
  extent 
  ; 
  and 
  it 
  is 
  therefore 
  necessary 
  

   to 
  carefully 
  find 
  out 
  by 
  experiment 
  the 
  most 
  suitable 
  capacity 
  

   for 
  each 
  coil 
  before 
  construction. 
  From 
  a 
  mere 
  consideration 
  

   of 
  minimizing 
  a 
  spark 
  at 
  the 
  interruptor 
  of 
  the 
  primary 
  circuit 
  

   one 
  might 
  be 
  induced 
  to 
  add 
  an 
  extra 
  capacity 
  to 
  the 
  circuit. 
  

   This 
  addition 
  of 
  capacity, 
  if 
  the 
  condenser 
  belonging 
  to 
  the 
  

   circuit 
  is 
  already 
  sufficient 
  or 
  too 
  great, 
  would 
  not 
  only 
  be 
  

   useless 
  but 
  will 
  do 
  harm. 
  What 
  amount 
  of 
  capacity, 
  then, 
  

   must 
  be 
  inserted 
  in 
  the 
  coil 
  ? 
  To 
  settle 
  this 
  question 
  is 
  not 
  a 
  

   simple 
  matter. 
  As 
  the 
  curves 
  show, 
  the 
  fittest 
  capacity 
  

   depends 
  upon 
  the 
  strength 
  of 
  the 
  primary 
  current, 
  and 
  conse- 
  

   quently 
  it 
  is 
  necessary 
  to 
  choose 
  a 
  capacity 
  giving 
  a 
  maximum 
  

   resonance-effect, 
  so 
  to 
  speak, 
  for 
  the 
  possible 
  strongest 
  current 
  

   allowable 
  to 
  the 
  primary 
  circuit. 
  In 
  the 
  two 
  induction-coils 
  

   examined 
  by 
  me 
  their 
  condensers 
  both 
  had 
  wrong 
  capacities. 
  

  

  For 
  on 
  measurement 
  the 
  capacity 
  of 
  the 
  condenser 
  in 
  the 
  

   first 
  coil 
  was 
  found 
  to 
  be 
  0*078, 
  while 
  that 
  of 
  the 
  second 
  was 
  

   0'75 
  microfarad. 
  Judging 
  from 
  the 
  results 
  of 
  my 
  observations 
  

   and 
  also 
  from 
  actual 
  experiments 
  with 
  those 
  condensers, 
  the 
  

   first 
  coil 
  had 
  a 
  smaller, 
  the 
  second 
  a 
  much 
  greater 
  capacity 
  

   than 
  was 
  necessary. 
  One 
  recent 
  valuable 
  research 
  on 
  induction- 
  

   coils 
  is 
  that 
  of 
  Colley 
  *, 
  who 
  examined 
  both 
  theoretically 
  and 
  

   experimentally 
  the 
  action 
  of 
  his 
  induction-coil. 
  

  

  A 
  few 
  months 
  ago 
  Walter 
  j 
  also 
  published 
  air 
  interesting 
  

   paper 
  on 
  the 
  same 
  subject. 
  In 
  fact, 
  he 
  found 
  that 
  there 
  is 
  a 
  

  

  * 
  Colley, 
  YVied. 
  Ann. 
  xliv. 
  p. 
  109 
  (1891). 
  

   t 
  Walter, 
  Wied. 
  Ann. 
  lxii. 
  p. 
  3C0 
  (1897). 
  

  

  