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  LXXIV. 
  Intelligence 
  and 
  Miscellaneous 
  Articles. 
  

  

  THE 
  PRODUCTION 
  OF 
  A 
  MAGNETIC 
  FIELD 
  BY 
  A 
  FLIGHT 
  OF 
  

   CHAEGED 
  PARTICLES. 
  BY 
  PROF. 
  R. 
  W. 
  WOOD. 
  

  

  IN 
  the 
  various 
  modifications 
  of 
  Rowland's 
  experiment 
  on 
  electric 
  

   convection, 
  centrifugal 
  force 
  places 
  an 
  upper 
  limit 
  to 
  the 
  

   attainable 
  velocity 
  of 
  the 
  moving 
  charge. 
  It 
  has 
  seemed 
  to 
  me 
  that 
  

   if 
  the 
  revolving 
  disk 
  could 
  be 
  abandoned, 
  and 
  a 
  flight 
  of 
  charged 
  

   particles 
  substituted, 
  for 
  it, 
  much 
  higher 
  velocities 
  could 
  be 
  obtained. 
  

   A 
  number 
  of 
  experiments 
  have 
  been 
  planned, 
  which 
  I 
  am 
  at 
  the 
  

   present 
  time 
  carrying 
  out 
  in 
  collaboration 
  with 
  Dr. 
  Harold 
  Pender. 
  

   The 
  first 
  one 
  has 
  already 
  yielded 
  positive 
  results, 
  a 
  deflexion 
  of 
  a 
  

   magnetic 
  needle 
  having 
  been 
  obtained 
  by 
  driving 
  a 
  cloud 
  of 
  charged 
  

   particles 
  of 
  solid 
  carbon 
  dioxide 
  through 
  a 
  long 
  glass 
  tube 
  placed 
  

   under 
  the 
  needle. 
  The 
  particles 
  become 
  charged 
  in 
  the 
  same 
  

   manner 
  as 
  the 
  steam-jet 
  in 
  the 
  hydroelectric 
  machine 
  of 
  Armstrong, 
  

   the 
  potential 
  being 
  so 
  high 
  that 
  sparks 
  over 
  a 
  centimetre 
  long 
  can 
  

   be 
  drawn 
  from 
  the 
  iron 
  cylinder 
  in 
  which 
  the 
  liquefied 
  gas 
  is 
  

   contained. 
  While 
  we 
  have 
  obtained 
  scale-deflexions 
  as 
  high 
  as 
  

   10 
  centimetres 
  with 
  the 
  tube 
  close 
  to 
  the 
  needle, 
  it 
  has 
  been 
  found 
  

   better 
  to 
  work 
  with 
  the 
  tube 
  about 
  2'5 
  cms. 
  below 
  the 
  needle, 
  in 
  

   which 
  case 
  the 
  deflexion 
  is 
  about 
  2 
  cms. 
  Reversing 
  the 
  direction 
  

   of 
  the 
  jet 
  invariably 
  reverses 
  the 
  direction 
  of 
  the 
  deflexion. 
  At 
  

   the 
  present 
  time 
  we 
  are 
  employing 
  two 
  glass 
  tubes 
  side 
  by 
  side 
  in 
  

   a 
  larger 
  tube, 
  the 
  space 
  between 
  being 
  filled 
  with 
  paraffin. 
  The 
  

   tubes 
  are 
  about 
  1*5 
  metre 
  long, 
  each 
  one 
  being 
  permanently 
  

   attached 
  to 
  a 
  cylinder 
  of 
  the 
  gas. 
  If 
  the 
  needle 
  is 
  deflected 
  by 
  a 
  

   stream 
  flowing 
  through 
  one 
  tube, 
  it 
  can 
  be 
  brought 
  nearly 
  back 
  to 
  

   its 
  original 
  position 
  by 
  setting 
  the 
  other 
  tube 
  in 
  action. 
  The 
  par- 
  

   ticles 
  appear 
  to 
  carry 
  positive 
  charges, 
  which 
  is 
  the 
  case 
  in 
  the 
  

   hydroelectric 
  machine, 
  and 
  the 
  direction 
  of 
  the 
  deflexion 
  is 
  the 
  

   same 
  as 
  when 
  an 
  electric 
  current 
  flows 
  from 
  the 
  carbon 
  to 
  the 
  zinc 
  

   in 
  the 
  direction 
  of 
  the 
  gas-jet. 
  As 
  yet 
  no 
  attempt 
  has 
  been 
  made 
  

   to 
  determine 
  experimentally 
  the 
  velocity 
  of 
  the 
  moving 
  charge. 
  

   About 
  a 
  pound 
  of 
  gas 
  escapes 
  in 
  20 
  seconds 
  through 
  the 
  tube, 
  

   which 
  has 
  a 
  bore 
  of 
  about 
  2-5 
  mm. 
  Taking 
  the 
  temperature 
  of 
  

   the 
  gas 
  as 
  >— 
  80°, 
  and 
  assuming 
  that 
  one 
  half 
  of 
  it 
  is 
  solidified 
  

   (doubtless 
  much 
  too 
  high 
  an 
  estimate), 
  the 
  calculated 
  velocity 
  is 
  

   not 
  far 
  from 
  2000 
  feet 
  per 
  second, 
  while 
  the 
  maximum 
  attainable 
  

   rim-speed 
  in 
  the 
  case 
  of 
  a 
  revolving 
  disk 
  is 
  less 
  than 
  300 
  feet. 
  To 
  

   calculate 
  the 
  velocity 
  it 
  will 
  be 
  necessary 
  to 
  know 
  not 
  only 
  the 
  

   amount 
  of 
  gas 
  solidified, 
  but 
  also 
  the 
  pressure-gradient 
  in 
  the 
  tube. 
  

   In 
  the 
  above 
  calculation 
  the 
  pressure 
  was 
  taken 
  as 
  that 
  of 
  the 
  

   atmosphere, 
  which 
  is 
  obviously 
  not 
  the 
  case, 
  though 
  the 
  error 
  

   introduced 
  may 
  be 
  partiaUy 
  offset 
  by 
  the 
  large 
  estimate 
  of 
  the 
  

   amount 
  of 
  solid 
  gas 
  present. 
  

  

  The 
  experiments 
  have 
  been 
  in 
  progress 
  for 
  but 
  a 
  few 
  days, 
  and 
  

   only 
  this 
  very 
  brief 
  preliminary 
  communication 
  is 
  possible 
  at 
  the 
  

   present 
  time. 
  

  

  