﻿in 
  Iron 
  by 
  Rapidly 
  Oscillating 
  Current- 
  fields. 
  503 
  

  

  through 
  a 
  circuit 
  containing 
  a 
  micrometer 
  spark-gap 
  S, 
  and 
  

   various 
  solenoids 
  and 
  coils, 
  L 
  l5 
  L 
  2 
  , 
  L 
  3 
  , 
  L. 
  The 
  jars 
  were 
  

   charged 
  by 
  connecting 
  to 
  the 
  secondary 
  terminals 
  of 
  an 
  

   induction-coil, 
  I, 
  through 
  the 
  primary 
  of 
  which 
  either 
  an 
  

   alternating 
  or 
  direct 
  current 
  was 
  passed. 
  The 
  three 
  solenoids 
  

  

  Fig. 
  1. 
  

  

  ■t 
  CHT 
  AIA//VJ 
  

  

  L 
  l5 
  L 
  2 
  , 
  and 
  L 
  3 
  were 
  made 
  exactly 
  alike, 
  and 
  each 
  had 
  the 
  

   same 
  number 
  of 
  turns. 
  Two 
  such 
  systems 
  of 
  solenoids 
  were 
  

   wound, 
  each 
  coil 
  of 
  the 
  first 
  system 
  having 
  645 
  turns, 
  and 
  of 
  

   the 
  second 
  system 
  140 
  turns, 
  the 
  insulation 
  of 
  the 
  D.c.c. 
  wire 
  

   being 
  in 
  both 
  cases 
  made 
  as 
  perfect 
  as 
  possible 
  by 
  being 
  

   drawn 
  through 
  melted 
  wax, 
  rubber 
  strips 
  being 
  also 
  placed 
  

   between 
  adjoining 
  rows 
  of 
  turns. 
  Various 
  other 
  coils, 
  L, 
  

   were 
  similarly 
  made, 
  but 
  of 
  such 
  dimensions 
  that 
  the 
  self- 
  

   inductions 
  could 
  be 
  accurately 
  calculated 
  by 
  means 
  of 
  

   Maxwell's 
  formula. 
  

  

  The 
  Braun's 
  tube 
  was 
  one 
  with 
  two 
  diaphragms, 
  and 
  

   having 
  the 
  improvements 
  suggested 
  by 
  Zenneck 
  *, 
  including 
  

   a 
  glass 
  screen 
  (instead 
  of 
  mica) 
  coated 
  with 
  CaW0 
  4 
  as 
  phos- 
  

   phorescent 
  material. 
  The 
  tube 
  was 
  excited 
  by 
  a 
  twenty-plate 
  

   Topler 
  influence-machine 
  driven 
  at 
  a 
  very 
  constant 
  rate 
  by 
  a 
  

   small 
  water-motor. 
  A 
  damp 
  thread 
  was 
  used 
  as 
  conductor 
  

   between 
  the 
  Topler 
  machine 
  and 
  the 
  anode 
  of 
  the 
  Braun's 
  

   tube, 
  which 
  was 
  connected 
  to 
  earth 
  in 
  order 
  to 
  eliminate 
  the 
  

   surface 
  charge 
  otherwise 
  present 
  on 
  the 
  surface 
  of 
  the 
  tube 
  

   in 
  the 
  neighbourhood 
  of 
  the 
  diaphragms, 
  and 
  to 
  give 
  increased 
  

   steadiness 
  to 
  the 
  phosphorescent 
  spot. 
  Two 
  of 
  the 
  three 
  

   similar 
  solenoids 
  (viz., 
  L 
  2 
  andL 
  3 
  , 
  see 
  sketch) 
  were 
  placed 
  sym- 
  

   metrically 
  with 
  respect 
  to 
  the 
  Braun'stube, 
  and 
  their 
  positions 
  

  

  * 
  J. 
  Zenneck, 
  Wied. 
  Ann. 
  lxix. 
  p. 
  844 
  (1899). 
  

  

  