﻿186 
  JOURNAL 
  OF 
  THE 
  WASHINGTON 
  ACADEMY 
  OF 
  SCIENCES 
  VOL. 
  12, 
  NO. 
  7 
  

  

  PROCEEDINGS 
  OF 
  THE 
  ACADEMY 
  AND 
  AFFILIATED 
  

  

  SOCIETIES 
  

  

  PHILOSOPHICAL 
  SOCIETY 
  

   858th 
  MEETING 
  

  

  The 
  858th 
  meeting 
  of 
  the 
  Philosophical 
  Society 
  of 
  Washington 
  was 
  held 
  in 
  

   the 
  Cosmos 
  Club 
  auditorium, 
  December 
  17, 
  1921 
  and 
  was 
  called 
  to 
  order 
  at 
  

   8.15 
  p.m. 
  by 
  President 
  Crittenden, 
  with 
  thirty-nine 
  persons 
  present. 
  The 
  

   program 
  was 
  as 
  follows: 
  

  

  W. 
  W. 
  CoBLENTz: 
  The 
  effective 
  temperature 
  of 
  stars 
  as 
  estimated 
  from 
  the 
  

   energy 
  distribution 
  in 
  the 
  complete 
  spectrum 
  (illustrated). 
  The 
  paper 
  was 
  

   discussed 
  by 
  Messrs. 
  Priest, 
  Hawksworth, 
  Foote, 
  Humphreys 
  and 
  

   Crittenden. 
  

  

  The 
  object 
  of 
  the 
  present 
  investigation 
  was: 
  (1) 
  to 
  test 
  new 
  stellar 
  ther- 
  

   mocouples; 
  (2) 
  to 
  verify 
  previous 
  measurements 
  of 
  stellar 
  radiation; 
  (3) 
  to 
  

   measure 
  the 
  radiation 
  intensities 
  of 
  bright 
  stars 
  in 
  the 
  region 
  of 
  hours 
  to 
  

   12 
  hours 
  of 
  right 
  ascension, 
  not 
  previously 
  measured; 
  and 
  (4) 
  to 
  determine 
  the 
  

   feasibility 
  of 
  the 
  method 
  of 
  obtaining 
  the 
  spectral 
  energy 
  distribution 
  of 
  stars 
  

   by 
  means 
  of 
  transmission 
  screens 
  which, 
  either 
  singly 
  or 
  in 
  combination, 
  are 
  

   placed 
  in 
  front 
  of 
  the 
  vacuum 
  thermocouple. 
  

  

  By 
  means 
  of 
  vacuum 
  thermocouples, 
  measurements 
  were 
  made 
  on 
  the 
  total 
  

   radiation 
  intensities 
  of 
  13 
  bright 
  stars 
  not 
  observed 
  in 
  1914, 
  thus 
  completing 
  

   the 
  survey 
  of 
  the 
  whole 
  sky. 
  A 
  total 
  of 
  30 
  celestial 
  objects 
  were 
  measured, 
  

   including 
  Venus 
  and 
  Mars. 
  

  

  By 
  means 
  of 
  a 
  series 
  of 
  transmission 
  screens 
  (of 
  yellow 
  and 
  red 
  glass, 
  of 
  water, 
  

   and 
  of 
  a 
  thick 
  plate 
  of 
  quartz), 
  wide 
  spectral 
  regions 
  were 
  isolated 
  and 
  the 
  

   radiation 
  intensities 
  in 
  the 
  spectrum 
  from 
  0.3/x 
  to 
  0.43ai; 
  0.43/^ 
  to 
  O.Gai; 
  0.6/x 
  

   to 
  1.4/x; 
  lAyi 
  to 
  4.1yu; 
  and 
  4.1/i 
  to 
  lO/x 
  were 
  determined. 
  In 
  this 
  manner 
  the 
  

   distribution 
  in 
  energy 
  in 
  the 
  spectra 
  of 
  16 
  stars 
  was 
  determined, 
  thus 
  obtaining 
  

   for 
  the 
  first 
  time 
  an 
  insight 
  into 
  the 
  radiation 
  intensities 
  in 
  the 
  complete 
  

   spectrum 
  of 
  a 
  star. 
  

  

  By 
  means 
  of 
  these 
  transmission 
  screens 
  it 
  was 
  found 
  that 
  in 
  the 
  B 
  and 
  A- 
  

   class 
  stars, 
  the 
  maximum 
  radiation 
  intensity 
  lies 
  in 
  the 
  ultra-violet 
  (0.3^i 
  to 
  

   0.4/i) 
  while 
  in 
  the 
  cooler, 
  K 
  and 
  M-class 
  stars, 
  the 
  maximum 
  emission 
  lies 
  

   at 
  0.7ai 
  to 
  0.9/i, 
  in 
  the 
  infra-red. 
  

  

  A 
  calculation 
  is 
  made 
  of 
  the 
  spectral 
  component 
  radiations 
  of 
  a 
  black 
  body 
  

   at 
  various 
  temperatures, 
  using 
  the 
  spectral 
  transmission 
  data 
  on 
  these 
  screens. 
  

   From 
  a 
  comparison 
  of 
  the 
  observed 
  and 
  the 
  calculated 
  spectral 
  rediation 
  

   components, 
  it 
  appears 
  that 
  the 
  black-body 
  temperature 
  {i. 
  e., 
  the 
  temperature 
  

   which 
  a 
  black 
  body 
  would 
  have 
  to 
  attain 
  in 
  order 
  to 
  emit 
  a 
  similar 
  relative 
  

   spectral 
  energy 
  distribution) 
  varies 
  from 
  3,000° 
  C. 
  for 
  red, 
  class 
  M 
  stars 
  

   (6,000° 
  for 
  the 
  yellow, 
  solar 
  type) 
  to 
  10,000° 
  or 
  perhaps 
  even 
  higher 
  for 
  blue, 
  

   class 
  B 
  stars. 
  

  

  The 
  observing 
  station 
  being 
  much 
  higher 
  than 
  that 
  previously 
  used 
  (7,300 
  

   feet 
  as 
  compared 
  with 
  4,000 
  feet), 
  the 
  atmospheric 
  scattering 
  of 
  light 
  was 
  

   greatly 
  reduced 
  ; 
  consequently, 
  when 
  the 
  water 
  cell 
  was 
  interposed 
  the 
  trans- 
  

   missions 
  in 
  the 
  violet 
  were 
  somewhat 
  higher 
  than 
  previously 
  observed. 
  How- 
  

   ever, 
  all 
  the 
  data 
  verify 
  previous 
  measurements 
  showing 
  that 
  red 
  stars 
  emit 
  

   3 
  to 
  4 
  times 
  as 
  much 
  infra-red 
  radiation 
  as 
  blue 
  stars 
  of 
  the 
  same 
  visual 
  mag- 
  

   nitude. 
  Moreover, 
  observations 
  made 
  on 
  the 
  same 
  night 
  (same 
  weather 
  

   conditions) 
  are 
  consistent 
  in 
  showing 
  small 
  gradations 
  in 
  the 
  infra-red 
  radia- 
  

  

  