﻿396 
  Prof. 
  B. 
  W. 
  Wood 
  on 
  the 
  Electrical 
  Resonance 
  of 
  

  

  current 
  flows 
  through 
  it 
  to 
  the 
  lead 
  electrode 
  M, 
  to 
  one 
  end 
  

   of 
  the 
  primary 
  of 
  the 
  coil, 
  and 
  out 
  by 
  the 
  other 
  end 
  to 
  the 
  

   negative 
  wire 
  of 
  the 
  mains. 
  By 
  the 
  movement 
  of 
  the 
  brush 
  

   one 
  can 
  regulate 
  the 
  amount 
  of 
  current 
  passing 
  through 
  the 
  

   primary. 
  

  

  The 
  number 
  of 
  interruptions 
  per 
  minute 
  can 
  be 
  changed 
  

   from 
  sixty 
  to 
  five 
  thousand 
  by 
  varying 
  the 
  speed 
  of 
  the 
  

   motor. 
  The 
  regulating 
  handle 
  of 
  the 
  motor 
  will 
  change 
  the 
  

   spark-length 
  of 
  the 
  coil 
  from 
  zero 
  to 
  thirty 
  inches 
  and 
  will 
  

   also 
  vary 
  the 
  quantity 
  of 
  the 
  discharge. 
  

  

  The 
  momentary 
  rush 
  of 
  current 
  through 
  the 
  primary 
  coil 
  is 
  

   probably 
  very 
  great, 
  although 
  the 
  ammeter 
  in 
  the 
  primary 
  

   circuit 
  indicates 
  not 
  more 
  than 
  5 
  or 
  10 
  amperes. 
  I 
  have 
  

   found 
  it 
  impossible 
  to 
  produce 
  a 
  spark 
  in 
  air 
  longer 
  than 
  

   seven 
  feet 
  by 
  means 
  of 
  a 
  storage-battery 
  and 
  a 
  Plante 
  

   transformer. 
  I 
  imagine 
  that 
  a 
  large 
  coil 
  built 
  on 
  the 
  above 
  

   principle 
  and 
  actuated 
  by 
  'very 
  powerful 
  commercial 
  currents 
  

   could 
  produce 
  sparks 
  much 
  longer 
  than 
  seven 
  feet. 
  Dynamos 
  

   are 
  now 
  built 
  of 
  a 
  size 
  far 
  exceeding 
  what 
  was 
  once 
  thought 
  

   possible. 
  The 
  needs 
  of 
  wireless 
  telegraphy 
  may 
  demand 
  a 
  

   corresponding 
  increase 
  in 
  the 
  size 
  of 
  induction-coils 
  : 
  and 
  

   the 
  coil 
  of 
  the 
  type 
  I 
  have 
  described, 
  without 
  a 
  condenser 
  and 
  

   with 
  a 
  liquid 
  break, 
  seems 
  to 
  be 
  the 
  type 
  for 
  the 
  future, 
  if 
  

   powerful 
  discharges 
  are 
  desired. 
  The 
  mechanical 
  break 
  and 
  

   the 
  primary 
  condenser 
  must 
  be 
  relegated 
  to 
  the 
  historical 
  

   physical 
  cabinet,, 
  

  

  Jefferson 
  Physical 
  Laboratory, 
  

   Harvard 
  University, 
  Cambridge, 
  U.S. 
  

  

  XL 
  IV. 
  A 
  suspected 
  case 
  of 
  the 
  Electrical 
  Resonance 
  of 
  Minute 
  

   Metal 
  Particles 
  for 
  Light-waves. 
  A 
  New 
  Type 
  of 
  

   Absorption. 
  By 
  R. 
  W. 
  Wood, 
  Professor 
  of 
  Experi- 
  

   mental 
  Physics 
  in 
  the 
  Johns 
  Hopkins 
  University*. 
  

  

  CERTAIN 
  experiments 
  on 
  which 
  I 
  have 
  been 
  engaged 
  of 
  

   late 
  have 
  led 
  me 
  to 
  believe 
  that 
  I 
  have 
  found 
  a 
  new 
  

   type 
  of 
  light 
  absorption, 
  which 
  it 
  may 
  be 
  possible 
  to 
  refer 
  to 
  

   the 
  electrical 
  resonance 
  of 
  small 
  metallic 
  particles 
  for 
  waves 
  

   of 
  light. 
  The 
  experiments 
  of 
  Garbasso 
  and 
  Aschkinass 
  have 
  

   shown 
  that 
  a 
  plate 
  of 
  glass 
  covered 
  with 
  uniformly 
  arranged 
  

   strips 
  of 
  tinfoil 
  of 
  equal 
  size, 
  which 
  serve 
  as 
  resonators, 
  

   shows 
  the 
  phenomenon 
  of 
  selective 
  transmission 
  and 
  reflexion 
  

   for 
  electromagnetic 
  waves 
  of 
  different 
  wave-lengths. 
  In 
  

   other 
  words, 
  a 
  plate 
  of 
  this 
  description 
  exhibits 
  the 
  electrical 
  

   analogy 
  of 
  surface-colour. 
  I 
  have 
  succeeded 
  in 
  producing 
  

   * 
  Communicated 
  by 
  the 
  Physical 
  Society 
  : 
  read 
  March 
  14, 
  1902. 
  

  

  