﻿Chemistry 
  and 
  Physics. 
  427 
  

  

  clusively 
  by 
  the 
  motion 
  of 
  the 
  magnets 
  that 
  all 
  the 
  tubes 
  are 
  

   closed 
  : 
  whenever 
  batteries 
  or 
  condensers 
  are 
  used, 
  open 
  tubes 
  are 
  

   present 
  in 
  the 
  field." 
  The 
  bearing 
  of 
  Professor 
  Thomson's 
  ex- 
  

   periments 
  on 
  the 
  aurora 
  is 
  extremely 
  interesting. 
  The 
  most 
  re- 
  

   markable 
  appearance 
  was 
  presented 
  when 
  the 
  discharge 
  passed 
  

   through 
  oxygen. 
  In 
  this 
  gas 
  the 
  bright 
  discharge 
  is 
  succeeded 
  by 
  

   a 
  phosphorescent 
  glow 
  which 
  lasts 
  for 
  a 
  considerable 
  time, 
  some- 
  

   times 
  for 
  more 
  than 
  a 
  minute. 
  The 
  spectrum 
  of 
  the 
  afterglow 
  is 
  

   a 
  continuous 
  one, 
  without 
  bright 
  lines. 
  The 
  only 
  gas 
  besides 
  oxy- 
  

   gen 
  which 
  shows 
  the 
  afterglow 
  is 
  air. 
  The 
  spectrum 
  of 
  the 
  air 
  

   glow 
  showed 
  bright 
  lines. 
  Professor 
  Thomson 
  is 
  continuing 
  his 
  

   investigation.— 
  Phil 
  Mag., 
  Oct., 
  1891, 
  pp. 
  323-336. 
  J. 
  t. 
  

  

  8. 
  Ratio 
  of 
  Electromagnetic 
  to 
  Electrostatic 
  units. 
  — 
  J. 
  J. 
  

   Thomson 
  and 
  G. 
  T. 
  C. 
  Searle 
  have 
  undertaken 
  a 
  redetermina- 
  

   tion 
  of 
  the 
  value 
  of 
  this 
  ratio. 
  A 
  complete 
  account 
  of 
  their 
  ex- 
  

   periments 
  can 
  be 
  found 
  in 
  Phil. 
  Trans., 
  Lond., 
  181 
  A., 
  pp. 
  583- 
  

   621, 
  1890. 
  The 
  value 
  obtained 
  is 
  v 
  = 
  2-9955'10 
  10 
  cm. 
  sec. 
  -1 
  . 
  

  

  J. 
  T. 
  

  

  9. 
  Expansion 
  of 
  Water. 
  — 
  A 
  useful 
  table 
  of 
  the 
  expansion 
  of 
  

   water 
  from 
  temperatures 
  0° 
  to 
  31° 
  is 
  given 
  by 
  W. 
  Marek. 
  — 
  Ann. 
  

   der 
  Physik 
  mid 
  Chemie, 
  No. 
  9, 
  1891, 
  p. 
  171. 
  j. 
  t. 
  

  

  10. 
  Experiments 
  in 
  Aerodynamics, 
  by 
  S. 
  P. 
  Langeey. 
  115 
  

   pp. 
  4to, 
  with 
  10 
  plates. 
  Washington, 
  1891 
  (Smithsonian 
  Contri- 
  

   butions 
  to 
  Knowledge, 
  801). 
  — 
  When 
  the 
  investigation 
  of 
  a 
  sub- 
  

   ject 
  like 
  that 
  of 
  "flying 
  machines" 
  — 
  at 
  once 
  so 
  stimulating 
  to 
  

   the 
  popular 
  imagination 
  and 
  yet 
  almost 
  an 
  ignis 
  fatuus 
  in 
  the 
  view 
  

   of 
  sober 
  minds 
  — 
  is 
  made 
  the 
  subject 
  of 
  careful 
  scientific 
  experi- 
  

   ment 
  in 
  skillful 
  hands 
  the 
  results 
  are 
  sure 
  to 
  be 
  of 
  unusual 
  

   interest 
  and 
  value. 
  This 
  is 
  eminently 
  true 
  of 
  Prof. 
  Langley's 
  

   investigations 
  in 
  aerodynamics 
  which 
  briefly 
  demonstrate 
  experi- 
  

   mentally 
  that 
  mechanical 
  flight 
  under 
  proper 
  direction 
  is 
  prac- 
  

   ticable 
  and 
  further 
  that 
  the 
  support 
  of 
  heavy 
  bodies 
  in 
  the 
  air, 
  

   combined 
  with 
  very 
  great 
  speeds 
  is 
  not 
  only 
  possible 
  but 
  within 
  

   the 
  reach 
  of 
  mechanical 
  means 
  now 
  available. 
  

  

  The 
  experiments 
  detailed 
  in 
  this 
  memoir 
  were 
  carried 
  on 
  at 
  

   Allegheny 
  Observatory 
  between 
  1887 
  and 
  1891. 
  They 
  describe 
  

   in 
  the 
  first 
  place 
  the 
  " 
  suspended 
  plane 
  " 
  — 
  a 
  thin 
  brass 
  plane 
  a 
  

   foot 
  square 
  weighing 
  two 
  pounds 
  hung 
  vertically 
  by 
  a 
  spring 
  

   from 
  a 
  surrounding 
  frame 
  and 
  capable 
  of 
  receiving 
  rapid 
  lateral 
  

   motion. 
  Briefly 
  expressed 
  the 
  important 
  result 
  of 
  the 
  experi- 
  

   ments 
  is 
  to 
  prove 
  that 
  the 
  downward 
  pressure 
  diminishes 
  as 
  the 
  

   velocity 
  increases, 
  the 
  spring 
  contracting 
  as 
  the 
  plane 
  is 
  carried 
  

   forward. 
  A 
  second 
  instrument 
  served 
  to 
  show 
  graphically 
  the 
  

   direction 
  of 
  the 
  total 
  resultant 
  pressure 
  on 
  a 
  square 
  inclined 
  

   plane 
  and 
  to 
  roughly 
  measure 
  its 
  amount 
  — 
  this 
  is 
  called 
  the 
  

   "resultant 
  pressure 
  recorder." 
  Still 
  another 
  instrument, 
  the 
  

   " 
  plane-dropper," 
  was 
  used 
  to 
  demonstrate 
  that 
  a 
  horizontal 
  

   plane 
  in 
  lateral 
  motion 
  requires 
  an 
  increased 
  time 
  for 
  its 
  descent, 
  

   and 
  also 
  to 
  measure 
  the 
  time 
  of 
  fall 
  for 
  different 
  planes 
  and 
  other 
  

   related 
  points, 
  thus 
  giving 
  the 
  soaring 
  speeds 
  of 
  wind-planes 
  

  

  