﻿214 
  Scientific 
  Intelligence. 
  

  

  SCIENTIFIC 
  INTELLIGENCE. 
  

  

  I. 
  Physics. 
  

  

  1. 
  Observations 
  from 
  the 
  Astrophysical 
  Observatory 
  connected 
  

   with 
  the 
  Smithsonian 
  Institution 
  at 
  Washington 
  / 
  by 
  C. 
  G-. 
  Abbot, 
  

   Aid 
  in 
  charge.* 
  

  

  (1) 
  On 
  the 
  dispersion 
  of 
  rock 
  salt. 
  — 
  This 
  subject 
  has 
  been 
  

   investigated 
  by 
  several 
  observers, 
  first 
  by 
  Langley 
  at 
  Allegheny 
  

   about 
  1886, 
  and 
  since 
  then 
  by 
  Julius, 
  Paschen, 
  Rubens 
  and 
  

   Snow, 
  and 
  others. 
  The 
  object 
  of 
  making 
  a 
  further 
  study 
  of 
  it 
  

   was 
  to 
  very 
  materially 
  increase 
  the 
  accuracy 
  of 
  determination 
  in 
  

   the 
  infra-red 
  portion 
  of 
  the 
  spectrum, 
  with 
  the 
  hope 
  of 
  establish- 
  

   ing 
  the 
  wave-lengths 
  of 
  the 
  infra-red 
  solar 
  absorption 
  lines 
  

   discovered 
  at 
  this 
  Observatory 
  to 
  a 
  degree 
  of 
  accuracy 
  corre- 
  

   sponding 
  with 
  the 
  accuracy 
  of 
  our 
  knowledge 
  of 
  their 
  minimum 
  

   deviations 
  in 
  the 
  spectrum 
  of 
  our 
  great 
  salt 
  prism. 
  There 
  

   appeared 
  to 
  be 
  strong 
  grounds 
  for 
  hope 
  of 
  succeeding 
  in 
  this 
  

   endeavor, 
  in 
  the 
  consideration 
  of 
  the 
  extraordinary 
  facilities 
  of 
  

   the 
  Observatory 
  for 
  such 
  a 
  research. 
  Accordingly, 
  the 
  appa- 
  

   ratus 
  was 
  made 
  ready 
  in 
  July 
  and 
  August 
  of 
  1898, 
  and 
  was 
  

   actually 
  tried 
  in 
  the 
  latter 
  part 
  of 
  August. 
  Active 
  work 
  was, 
  

   however, 
  deferred 
  until 
  the 
  latter 
  part 
  of 
  December, 
  and 
  was 
  

   done 
  chiefly 
  in 
  January 
  and 
  February 
  of 
  1899. 
  While 
  the 
  

   method 
  and 
  results 
  will 
  be 
  fully 
  described 
  in 
  the 
  forthcoming 
  

   publication, 
  a 
  brief 
  statement 
  will 
  be 
  appropriate 
  here. 
  

  

  The 
  radiations 
  of 
  the 
  sun 
  were 
  used 
  as 
  the 
  source 
  of 
  energy 
  

   up 
  to 
  a 
  wave-length 
  of 
  4^, 
  but 
  from 
  this 
  point 
  to 
  6.5/* 
  (where 
  the 
  

   research 
  was 
  stopped, 
  partly 
  because 
  the 
  grating 
  used 
  was 
  no 
  

   longer 
  applicable, 
  and 
  partly 
  because 
  further 
  progress 
  was 
  of 
  no 
  

   particular 
  interest) 
  the 
  radiations 
  of 
  an 
  iron-gauze 
  mantle 
  heated 
  

   in 
  a 
  Kitson 
  lamp 
  (burning 
  vaporized 
  petroleum) 
  were 
  employed. 
  

   The 
  radiations, 
  from 
  whichever 
  source, 
  fell 
  first 
  upon 
  a 
  slit 
  10 
  

   centimeters 
  high, 
  then 
  upon 
  a 
  concave 
  diffraction 
  grating, 
  and 
  

   then 
  upon 
  the 
  slit 
  of 
  the 
  spectro-bolometer, 
  which 
  remained 
  

   practically 
  as 
  used 
  in 
  taking 
  solar 
  holographs. 
  The 
  grating 
  

   apparatus 
  being 
  mounted 
  according 
  to 
  Rowland's 
  well-known 
  

   device, 
  radiations 
  whose 
  wave-lengths 
  were 
  multiples 
  of 
  each 
  

   other 
  fell 
  upon 
  the 
  slit 
  of 
  the 
  spectro-bolometer, 
  and 
  passed 
  

   through 
  to 
  have 
  their 
  prismatic 
  deviations 
  determined. 
  For 
  

   instance, 
  if 
  the 
  apparatus 
  was 
  adjusted 
  so 
  that 
  the 
  well-marked 
  

   line 
  of 
  wave-length 
  0.5616/x 
  in 
  the 
  fourth-order 
  spectrum 
  was 
  

   found 
  by 
  visual 
  observation 
  falling 
  at 
  the 
  center 
  of 
  the 
  slit, 
  then 
  

   it 
  would 
  be 
  certain 
  that 
  the 
  radiations 
  of 
  the 
  following 
  multiples 
  

   of 
  this 
  wave-length 
  also 
  fell 
  there 
  : 
  4/3, 
  4/2, 
  and 
  4/1. 
  The 
  two 
  

   latter 
  would 
  be 
  well 
  within 
  the 
  infra-red. 
  

  

  Suppose, 
  now, 
  the 
  driving 
  clock 
  of 
  the 
  spectro-bolographic 
  

   apparatus 
  to 
  be 
  started, 
  and 
  a 
  curve 
  automatically 
  produced 
  just 
  

   *From 
  the 
  Report 
  of 
  Professor 
  S. 
  P. 
  Langley, 
  mentioned 
  on 
  p. 
  233. 
  

  

  