﻿Minute 
  Metal 
  Particles 
  for 
  Light-waves. 
  401 
  

  

  appearances 
  of 
  the 
  films 
  by 
  reflected 
  and 
  transmitted 
  light, 
  

   the 
  spectral 
  analysis 
  of 
  the 
  light, 
  the 
  polarization 
  effects, 
  and 
  

   the 
  very 
  remarkable 
  temperature 
  changes. 
  

  

  If 
  the 
  metal 
  is 
  heated 
  at 
  one 
  end 
  of 
  a 
  rather 
  long 
  tapering 
  

   bulb, 
  the 
  colour 
  is 
  most 
  intense 
  near 
  the 
  metal 
  and 
  gradually 
  

   fades 
  away 
  to 
  nothing 
  at 
  the 
  other 
  end 
  of 
  the 
  bulb. 
  If 
  the 
  

   bulb 
  is 
  placed 
  in 
  strong 
  sunlight 
  with 
  a 
  black 
  background, 
  it 
  

   is 
  seen 
  that 
  in 
  some 
  places 
  where 
  the 
  deposit 
  is 
  too 
  slight 
  to 
  

   show 
  much 
  colour 
  by 
  transmission 
  the 
  light 
  is 
  scattered 
  or 
  

   ditfused, 
  and 
  this 
  diffused 
  light 
  is 
  coloured. 
  The 
  claret- 
  

   coloured 
  or 
  purple 
  film, 
  where 
  the 
  deposit 
  is 
  slight, 
  scatters 
  a 
  

   green 
  light, 
  the 
  surface 
  appearing 
  as 
  if 
  fluorescent. 
  Now 
  the 
  

   spectrum 
  of 
  the 
  transmitted 
  light 
  in 
  these 
  purple 
  films 
  has 
  a 
  

   heavy 
  absorption-band 
  in 
  the 
  yellow-green, 
  consequently 
  the 
  

   scattered' 
  light 
  is 
  the 
  complementary 
  colour 
  of 
  the 
  transmitted. 
  

   If 
  the 
  film 
  is 
  greenish 
  blue, 
  the 
  scattered 
  light 
  is 
  reddish. 
  

   The 
  microscope 
  shows 
  that 
  in 
  these 
  deposits, 
  which 
  have 
  the 
  

   power 
  of 
  scattering 
  light, 
  the 
  individual 
  particles 
  are 
  rather 
  

   widely 
  separated, 
  that 
  is, 
  the 
  distance 
  between 
  them 
  is 
  large 
  

   in 
  comparison 
  to 
  their 
  diameters. 
  I 
  shall 
  speak 
  of 
  this 
  light 
  

   as 
  the 
  " 
  fluorescent" 
  light, 
  to 
  distinguish 
  it 
  from 
  the 
  light 
  

   scattered 
  by 
  the 
  large 
  particles, 
  which 
  is 
  not 
  coloured 
  except 
  

   by 
  diffraction. 
  This 
  light, 
  which 
  gives 
  the 
  bulbs 
  a 
  slightly 
  

   silky 
  lustre 
  where 
  the 
  particles 
  are 
  large, 
  I 
  shall 
  call 
  diffused 
  

   light. 
  

  

  Returning 
  now 
  to 
  the 
  fluorescent 
  light 
  : 
  in 
  the 
  case 
  of 
  the 
  

   purple 
  films, 
  the 
  appearance 
  of 
  a 
  bulb 
  in 
  strong 
  light 
  is 
  very 
  

   much 
  as 
  if 
  certain 
  portions 
  of 
  its 
  interior 
  surface 
  had 
  been 
  

   painted 
  over 
  with 
  a 
  solution 
  of 
  fluorescein. 
  No 
  trace 
  of 
  

   regular 
  reflexion 
  is 
  shown 
  by 
  these 
  films, 
  except 
  of 
  course 
  

   the 
  reflexion 
  due 
  to 
  the 
  glass. 
  The 
  particles 
  are 
  so 
  far 
  a] 
  tart 
  

   that 
  they 
  apparently 
  act 
  as 
  independent 
  sources, 
  the 
  inter- 
  

   ference 
  necessary 
  for 
  rectilinear 
  propagation 
  not 
  being 
  present. 
  

   If 
  the 
  incident 
  light 
  is 
  polarized, 
  the 
  fluorescent 
  light 
  is 
  also 
  

   polarized, 
  which 
  is 
  not 
  the 
  case 
  for 
  ordinary 
  diffuse 
  reflexion. 
  

   On 
  the 
  resonance 
  theory, 
  we 
  may 
  regard 
  this 
  fluorescent 
  light 
  

   as 
  the 
  energy 
  radiated 
  from 
  the 
  resonators, 
  as 
  a 
  result 
  of 
  

   their 
  forced 
  vibrations. 
  Passing 
  now 
  to 
  a 
  part 
  of 
  the 
  film 
  

   where 
  the 
  colour 
  of 
  the 
  transmitted 
  light 
  is 
  deeper, 
  we 
  find 
  

   that 
  there 
  is 
  no 
  longer 
  any 
  trace 
  of 
  this 
  fluorescent 
  light. 
  

   The 
  colour 
  absent 
  in 
  the 
  transmitted 
  light 
  is 
  now 
  regularly 
  

   reflected, 
  the 
  particles 
  being 
  so 
  close 
  together 
  that 
  interference, 
  

   as 
  imagined 
  by 
  Huygens, 
  takes 
  place. 
  In 
  strong 
  sunlight, 
  

   this 
  portion 
  of 
  the 
  film 
  shows 
  neither 
  the 
  fluorescent 
  nor 
  the 
  

   diffused 
  (diffracted) 
  light. 
  Except 
  at 
  the 
  spot 
  where 
  the 
  

   regularly 
  reflected 
  image 
  of 
  the 
  source 
  of 
  light 
  appears, 
  it 
  is 
  

  

  