﻿100 
  Messrs. 
  Trowbridge 
  and 
  Burbank 
  on 
  

  

  in 
  thickness, 
  and 
  the 
  charging 
  and 
  discharging 
  method 
  is 
  a 
  

   complete 
  departure 
  from 
  that 
  adopted 
  by 
  Piante. 
  All 
  forms 
  

   of 
  rotating 
  cylinders 
  carrying 
  contact-pieces 
  were 
  abandoned, 
  

   and 
  two 
  lever-arms 
  were 
  used 
  to 
  charge 
  the 
  condensers 
  in 
  

   parallel, 
  and 
  then 
  to 
  discharge 
  in 
  series. 
  Great 
  uniformity 
  

   of 
  action 
  was 
  thus 
  secured. 
  

  

  The 
  sparks 
  produced 
  by 
  the 
  apparatus 
  have 
  great 
  disruptive 
  

   effects, 
  and 
  produce 
  reports 
  like 
  the 
  discharge 
  of 
  a 
  pistol. 
  

   The 
  electrostatic 
  field 
  in 
  the 
  neighbourhood 
  of 
  the 
  terminals 
  

   is 
  very 
  intense, 
  and 
  the 
  wires 
  leading 
  to 
  the 
  spark-gap 
  emit 
  

   brush-discharges 
  which 
  extend 
  at 
  least 
  12 
  inches 
  from 
  the 
  

   surface 
  of 
  the 
  wire. 
  I 
  was 
  interested 
  to 
  observe 
  the 
  effect 
  

   of 
  such 
  powerful 
  discharges 
  through 
  Crookes-tubes, 
  and 
  

   therefore 
  set 
  up 
  a 
  tube 
  which 
  had 
  been 
  exhausted 
  to 
  such 
  a 
  

   degree 
  that 
  sparks 
  of 
  8 
  inches 
  in 
  length 
  preferred 
  to 
  pass 
  

   through 
  the 
  air 
  from 
  terminal 
  to 
  terminal 
  of 
  the 
  tube 
  rather 
  

   than 
  to 
  pass 
  through 
  the 
  rarefied 
  space. 
  The 
  disruptive 
  

   discharge 
  produced 
  by 
  the 
  machine 
  passed 
  readily 
  through 
  

   such 
  a 
  tube, 
  and 
  showed 
  the 
  A'-rays 
  with 
  great 
  brilliancy: 
  

   moreover, 
  the 
  degree 
  of 
  rarefication 
  of 
  the 
  tube 
  was 
  not 
  

   sensibly 
  altered 
  by 
  single 
  discharges 
  of 
  such 
  high 
  electro- 
  

   motive 
  force. 
  

  

  The 
  results 
  so 
  far 
  obtained 
  by 
  the 
  employment 
  of 
  this 
  

   apparatus 
  prove 
  (1) 
  that 
  the 
  length 
  of 
  spark 
  is 
  proportional 
  

   to 
  the 
  electromotive 
  force 
  ; 
  (2) 
  rarefied 
  spaces 
  hitherto 
  con- 
  

   sidered 
  too 
  high 
  vacua 
  to 
  conduct 
  electricity 
  cease 
  to 
  act 
  like 
  

   such 
  vacua 
  to 
  very 
  high 
  electromotive 
  force. 
  

  

  Jefferson 
  Physical 
  Laboratory, 
  

   Harvard 
  Universsty, 
  Cambridge, 
  U.S. 
  

  

  IX. 
  Phosphorescence 
  'produced 
  by 
  Electrification. 
  

   By 
  John 
  Trowbridge 
  and 
  John 
  E. 
  Etjrbank*. 
  

  

  "T^ARIOUS 
  investigators 
  have 
  stated 
  that 
  the 
  «r-rays 
  can 
  

   T 
  communicate 
  an 
  electrical 
  charge 
  to 
  bodies. 
  We 
  were 
  

   interested 
  to 
  discover 
  whether 
  this 
  statement 
  could 
  be 
  verified 
  

   by 
  means 
  of 
  the 
  phenomenon 
  of 
  phosphorescence. 
  When 
  

   fluorite, 
  in 
  the 
  state 
  of 
  a 
  comparatively 
  coarse 
  powder, 
  is 
  

   heated 
  to 
  a 
  low 
  red 
  heat 
  for 
  about 
  an 
  hour, 
  it 
  loses 
  completely 
  

   its 
  power 
  of 
  phosphorescing 
  under 
  the 
  effect 
  of 
  a 
  low 
  red 
  heat; 
  

   if 
  it 
  is 
  then 
  electrified 
  by 
  means 
  of 
  the 
  brush-discharge 
  of 
  an 
  

   electrical 
  machine 
  and 
  then 
  submitted 
  to 
  a 
  low 
  red 
  heat 
  it 
  

   suddenly 
  phosphoresces. 
  In 
  this 
  connexion 
  it 
  is 
  interesting 
  

  

  * 
  Communicated 
  by 
  the 
  Authors. 
  

  

  