﻿534 
  

  

  Prof. 
  D. 
  N. 
  Mallik 
  on 
  Magnetic 
  

  

  discharges 
  in 
  air 
  can 
  be 
  derived 
  from 
  the 
  curves 
  (fig. 
  8, 
  

   I. 
  & 
  II.). 
  In 
  these, 
  pressures 
  in 
  millimetres 
  of 
  mercury 
  

  

  Fia\ 
  8.— 
  I. 
  & 
  II. 
  

  

  S50 
  

  

  I 
  

  

  *30 
  

  

  

  

  

  

  

  

  

  

  / 
  

  

  

  

  

  

  

  

  

  i 
  

  

  r 
  

  

  / 
  

  

  

  

  

  

  

  

  

  

  / 
  

  

  

  

  

  

  

  

  

  

  

  

  

  

  

  

  y% 
  

  

  

  

  

  

  

  

  y 
  

  

  ^ 
  

  

  

  

  

  

  

  y 
  

  

  * 
  

  

  V 
  

  

  

  

  

  

  

  0(, 
  

  

  f 
  

  

  

  

  

  

  

  

  

  60 
  70 
  

  

  ELECTfTOST/ITlC 
  u/virs 
  

  

  10 
  ^0 
  30 
  40 
  50 
  

  

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  F-OTEHTI/tL 
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  OF 
  THE 
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   II 
  - 
  - 
  4- 
  CELLS 
  - 
  - 
  - 
  ..-••. 
  

  

  are 
  ordinates, 
  and 
  the 
  corresponding 
  potential-differences 
  

   between 
  the 
  electrodes 
  in 
  electrostatic 
  units 
  are 
  abscissse. 
  

  

  These 
  curves 
  were 
  obtained 
  by 
  measuring 
  the 
  lengths 
  of 
  

   sparks 
  between 
  two 
  brass 
  spheres 
  of 
  3 
  cm. 
  diameter 
  in 
  

   parallel 
  with 
  the 
  discharge 
  tube 
  and 
  deducing 
  the 
  corre- 
  

   sponding 
  potential-difference 
  from 
  the 
  table 
  given 
  at 
  p. 
  461 
  

   of 
  J. 
  J 
  . 
  Thomson's 
  ' 
  Conduction 
  of 
  Electricity 
  through 
  

   Gases,' 
  2nd 
  ed., 
  by 
  interpolation. 
  

  

  12. 
  It 
  will 
  be 
  seen 
  that 
  we 
  may 
  roughly 
  distinguish 
  four 
  

   portions 
  in 
  each 
  curve, 
  AB, 
  BC, 
  CD, 
  DE. 
  The 
  first 
  portion 
  

   (AB), 
  which 
  is 
  very 
  nearly 
  straight, 
  corresponds 
  to 
  the 
  

   " 
  spray 
  " 
  discharge. 
  As 
  the 
  pressure 
  decreases 
  the 
  character 
  

   of 
  the 
  discharge 
  changes 
  ; 
  it 
  forms 
  into 
  a 
  band 
  by 
  the 
  con- 
  

   fluence 
  of 
  most 
  of 
  the 
  discrete 
  streams. 
  This 
  is 
  indicated 
  

   by 
  the 
  bend 
  in 
  the 
  curve 
  at 
  B. 
  

  

  After 
  this, 
  the 
  relation 
  between 
  pressure 
  and 
  potential- 
  

   difference 
  is 
  given 
  by 
  a 
  straight 
  line 
  BC. 
  Throughout 
  this 
  

   stage, 
  the 
  discharge 
  is 
  in 
  the 
  form 
  of 
  a 
  band 
  of 
  light 
  which 
  

   rotates 
  according 
  to 
  the 
  law 
  pco 
  = 
  constant. 
  Gradually 
  the 
  

  

  