﻿480 
  Mr. 
  B. 
  S. 
  Cohen 
  on 
  Production 
  of 
  Small 
  

  

  is 
  not 
  the 
  case, 
  and 
  as 
  he 
  then 
  introduces 
  hypothetical 
  values 
  

   o£ 
  n, 
  the 
  reciprocal 
  of 
  the 
  fraction 
  of 
  air 
  radiation 
  radiated 
  

   downwards, 
  the 
  attempt 
  cannot 
  be 
  regarded 
  as 
  successful. 
  

   The 
  band 
  absorption 
  which 
  alone 
  communicates 
  heat 
  to 
  the 
  

   air 
  directly, 
  remains 
  but 
  a 
  fraction 
  of 
  the 
  total 
  depletion 
  even 
  

   at 
  sunset. 
  I 
  doubt 
  if 
  the 
  band 
  absorption 
  ever 
  exceeds 
  0*5. 
  

  

  Since 
  no 
  reasonable 
  modification 
  of 
  the 
  constants 
  will 
  

   enable 
  the 
  simple 
  formula 
  for 
  a 
  glass 
  greenhouse 
  to 
  fit 
  the 
  

   atmospheric 
  conditions 
  on 
  our 
  earth, 
  the 
  formula 
  is 
  in- 
  

   applicable 
  to 
  problems 
  of 
  planetary 
  temperature 
  without 
  

   extensive 
  modifications, 
  except 
  perhaps 
  in 
  the 
  conceivable 
  

   case 
  of 
  a 
  special 
  reflective 
  atmosphere. 
  

   AVestwood, 
  Massachusetts, 
  

   February 
  7, 
  1908. 
  

  

  XLII. 
  The 
  Production 
  of 
  Small 
  Variable 
  Frequency 
  Alternating 
  

   Currents 
  suitable 
  for 
  Telephonic 
  and 
  other 
  Measurements. 
  

   By 
  B. 
  S. 
  Cohen 
  *'. 
  

  

  [Plates 
  XVI. 
  -XIX.] 
  

  

  TNTRODUCTION.— 
  -The 
  devices 
  described 
  in 
  the 
  latter 
  

   part 
  of 
  this 
  paper 
  are 
  the 
  outcome 
  of 
  experiments 
  carried 
  

   out 
  in 
  the 
  Investigation 
  Branch 
  of 
  the 
  Engineering 
  Depart- 
  

   ment 
  of 
  the 
  National 
  Telephone 
  Company, 
  in 
  order 
  to 
  obtain 
  

   suitable 
  alternating 
  currents 
  both 
  of 
  simple 
  and 
  complex 
  

   wave 
  form 
  to 
  act 
  as 
  substitutes 
  for 
  the 
  voice 
  in 
  telephonic 
  

   measurements. 
  Although 
  primarily 
  designed 
  for 
  this 
  purpose, 
  

   it 
  is 
  considered 
  possible 
  that 
  the 
  apparatus 
  to 
  be 
  described 
  is 
  

   capable 
  of 
  more 
  extended 
  use. 
  

  

  A 
  short 
  summary 
  of 
  the 
  methods 
  known 
  to 
  the 
  author 
  of 
  

   obtaining 
  small 
  alternating 
  currents 
  of 
  the 
  kind 
  suitable 
  for 
  

   telephonic 
  measurements 
  may 
  prove 
  of 
  interest 
  as 
  an 
  intro- 
  

   duction. 
  

  

  Statement 
  of 
  the 
  problem. 
  — 
  The 
  ordinary 
  telephonic 
  current 
  

   is 
  a 
  few 
  milliamperes 
  at 
  a 
  potential 
  of 
  about 
  2 
  to 
  10 
  volts 
  

   and 
  is 
  of 
  complex 
  wave 
  form. 
  The 
  frequency 
  of 
  the 
  funda- 
  

   mental 
  harmonic 
  generally 
  lies 
  between 
  100 
  and 
  300 
  complete 
  

   periods 
  per 
  second, 
  i. 
  e. 
  it 
  varies 
  from 
  100 
  — 
  - 
  to 
  300~, 
  'the 
  

   highest 
  harmonic 
  having 
  a 
  frequency 
  of 
  4000-^- 
  to 
  5000^, 
  

   although 
  all 
  harmonics 
  above 
  1500~ 
  are 
  comparatively 
  un- 
  

   important. 
  The 
  average 
  frequency 
  of 
  the 
  whole 
  wave 
  is 
  

   about 
  800^-. 
  From 
  consideration 
  of 
  these 
  data 
  it 
  follows 
  that 
  

   the 
  ideal 
  device 
  for 
  supplying 
  such 
  alternating 
  current 
  is 
  

   one 
  which 
  will 
  give 
  currents 
  of 
  any 
  frequency 
  lying 
  between 
  

   100-— 
  to 
  500^-, 
  singly 
  or 
  in 
  combination. 
  The 
  output 
  of 
  this 
  

  

  * 
  Communicated 
  by 
  the 
  Physical 
  Society 
  : 
  read 
  May 
  22, 
  1908. 
  

  

  