﻿Diffraction 
  of 
  Light 
  by 
  Cylinders 
  of 
  Large 
  Radius, 
  79 
  

  

  are 
  somewhat 
  analogous 
  to 
  coupled 
  electrical 
  circuits 
  with 
  

   different 
  inductances 
  or 
  different 
  periods. 
  

  

  2. 
  The 
  case 
  of 
  masses 
  20 
  : 
  1 
  is 
  seen 
  to 
  be 
  very 
  nearly 
  that 
  

   of 
  forced 
  vibrations 
  in 
  which 
  the 
  light 
  bob 
  is 
  driven 
  by 
  

   receiving 
  energy 
  from 
  the 
  heavy 
  bob 
  or 
  driver, 
  while 
  the 
  

   latter's 
  loss, 
  though 
  equal 
  in 
  energy, 
  entails 
  only 
  a 
  very 
  

   small 
  decrease 
  of 
  amplitude. 
  The 
  case 
  of 
  masses 
  as 
  5 
  : 
  1 
  is 
  

   about 
  midway 
  in 
  character 
  between 
  that 
  of 
  20 
  : 
  1 
  and 
  equal 
  

   masses. 
  Eighteen 
  photographic 
  reproductions 
  of 
  double 
  

   traces 
  are 
  given 
  for 
  unequal 
  masses. 
  

  

  3. 
  It 
  was 
  noticeable 
  on 
  one 
  of 
  the 
  traces 
  that 
  the 
  light 
  

   bob 
  showed 
  diminution 
  of 
  amplitude 
  as 
  the 
  trace 
  proceeded. 
  

   This 
  led 
  to 
  taking 
  resistance 
  into 
  account 
  in 
  the 
  equation 
  of 
  

   motion. 
  It 
  was 
  also 
  necessary 
  to 
  determine 
  experimentally 
  

   the 
  actual 
  damping 
  of 
  the 
  light 
  bob 
  when 
  vibrating 
  sepa- 
  

   rately. 
  The 
  theory 
  thus 
  developed 
  and 
  numerically 
  applied 
  

   fitted 
  the 
  observed 
  facts. 
  

  

  4. 
  In 
  the 
  case 
  of 
  unequal 
  lengths 
  but 
  equal 
  masses, 
  a 
  

   feebler 
  response 
  and 
  a 
  shorter 
  beat 
  cycle 
  may 
  naturally 
  be 
  

   expected 
  than 
  if 
  mistuning 
  were 
  absent. 
  Both 
  these 
  effects 
  

   are 
  quite 
  striking 
  with 
  loose 
  couplings. 
  But 
  with 
  the 
  tighter 
  

   couplings 
  the 
  effect 
  of 
  mistuning 
  is 
  practically 
  unnoticeable. 
  

   The 
  theory 
  agrees 
  with 
  this 
  experimental 
  result. 
  Nine 
  sets 
  

   of 
  double 
  traces 
  are 
  given 
  for 
  the 
  unequal 
  periods. 
  

  

  5. 
  It 
  is 
  hoped 
  that 
  these 
  methods 
  may 
  be 
  shortly 
  applied 
  

   to 
  the 
  illustration 
  of 
  important 
  phenomena 
  in 
  other 
  branches 
  

   of 
  Physics. 
  

  

  Nottingham, 
  

   Nov. 
  19, 
  1917. 
  

  

  IX. 
  On 
  the 
  Diffraction 
  of 
  Light 
  by 
  Cylinders 
  of 
  Large 
  Radius. 
  

   By 
  Nalinimohan 
  Basu, 
  M.Sc, 
  Sir 
  Rashbehari 
  Ghosh 
  

   Research 
  Scholar 
  in 
  the 
  University 
  of 
  Calcutta 
  *. 
  

  

  [Plate 
  III.] 
  

  

  Lntroduction. 
  

  

  1. 
  C. 
  F. 
  Brush 
  has 
  recently 
  published 
  a 
  paper 
  containing 
  

   some 
  interesting 
  observations 
  on 
  the 
  diffraction 
  of 
  light 
  by 
  

   the 
  edge 
  of 
  a 
  cylindrical 
  obstacle 
  f. 
  Brush 
  worked 
  with 
  

  

  * 
  Communicated 
  by 
  Prof. 
  C. 
  V. 
  Raman. 
  

  

  f 
  u 
  Some 
  Diffraction 
  Phenomena: 
  Superposed 
  Fringes," 
  bv 
  C. 
  F. 
  Brush, 
  

   Proceedings 
  of 
  the 
  American 
  Philosophical 
  Society, 
  1913," 
  pp. 
  276-282. 
  

   See 
  also 
  < 
  Science 
  Abstracts,' 
  No. 
  1810 
  (1913). 
  

  

  