﻿.342 
  Prof. 
  W. 
  G. 
  Driffield 
  on 
  tl 
  

  

  le 
  

  

  condense 
  in 
  contact 
  with 
  the 
  cathode 
  adhere 
  to 
  it 
  by 
  reason 
  of 
  

   cohesive 
  forces, 
  while 
  some 
  few, 
  although 
  negatively 
  charged, 
  

   may 
  be 
  sufficiently 
  near 
  to 
  be 
  attracted 
  by 
  it. 
  The 
  same 
  

   influences 
  are 
  at 
  work 
  upon 
  the 
  surface 
  of 
  the 
  anode, 
  but 
  

   the 
  electrons 
  are 
  bound 
  by 
  the 
  positive 
  charges 
  there. 
  The 
  

   growth 
  itself, 
  however, 
  when 
  once 
  begun 
  takes 
  part 
  in 
  this 
  

   action, 
  and 
  condensation 
  of 
  metallic 
  deposit 
  ensues 
  upon 
  its 
  

   apex. 
  

  

  (3) 
  Further, 
  the 
  predominating 
  influence 
  of 
  the 
  cathode 
  

   is 
  assisted 
  by 
  the 
  action 
  of 
  ultra-violet 
  radiation 
  upon 
  the 
  

   particles 
  in 
  the 
  vapour 
  above 
  the 
  arc, 
  which 
  promotes 
  the 
  

   emission 
  of 
  electrons 
  from 
  them. 
  The 
  particles 
  are 
  con- 
  

   sequently 
  left 
  with 
  a 
  positive 
  charge, 
  which 
  persists 
  until 
  a 
  

   collision 
  occurs 
  between 
  them 
  and 
  one 
  of 
  the 
  vagrant 
  electrons. 
  

   Though 
  not 
  permanently 
  positive, 
  there 
  is 
  on 
  the 
  whole 
  an 
  

   increase 
  in 
  the 
  number 
  of 
  ions 
  which 
  are 
  at 
  any 
  instant 
  

   charged 
  with 
  that 
  sign, 
  and 
  these 
  are 
  more 
  readily 
  swept 
  

   upon 
  the 
  pole 
  than 
  are 
  the 
  neutral 
  masses. 
  Ehrenhaft 
  does 
  

   not 
  remark 
  an 
  excess 
  of 
  positive 
  ions, 
  but 
  as 
  the 
  gases 
  in 
  his 
  

   experiment 
  appear 
  to 
  have 
  been 
  sucked 
  from 
  one 
  part 
  of 
  

   his 
  apparatus 
  to 
  another, 
  recombination 
  may 
  have 
  taken 
  place 
  

   after 
  the 
  particles 
  had 
  ceased 
  to 
  be 
  under 
  the 
  influence 
  of 
  the 
  

   ultra-violet 
  light. 
  

  

  The 
  progress 
  of 
  the 
  growths. 
  — 
  Once 
  having 
  started, 
  the 
  

   growth 
  extends 
  by 
  " 
  the 
  action 
  of 
  contiguous 
  particles,'' 
  the 
  

   first 
  small 
  deposit 
  acting 
  like 
  a 
  point 
  and 
  exerting 
  a 
  superior 
  

   attraction 
  upon 
  the 
  vagrant 
  ions. 
  The 
  growths 
  extend 
  out- 
  

   wards 
  along 
  a 
  line 
  of 
  force, 
  and 
  while 
  in 
  a 
  homogeneous 
  

   vapour 
  there 
  should 
  be 
  nothing 
  to 
  deviate 
  the 
  growths 
  from 
  

   a 
  straight 
  path 
  from 
  the 
  cathode 
  to 
  the 
  anode, 
  some 
  irre- 
  

   gularities 
  in 
  the 
  deposit 
  naturally 
  occur 
  where 
  particles 
  of 
  

   various 
  sizes 
  and 
  of 
  doubtful 
  sphericity 
  abound, 
  and 
  when 
  

   an 
  irregular 
  mass 
  is 
  deposited 
  several 
  fresh 
  shoots 
  start 
  out 
  

   inclined 
  to 
  the 
  main 
  stem. 
  These 
  laterals 
  are 
  in 
  general 
  at 
  

   equal 
  distances 
  from 
  one 
  another 
  and 
  perpendicular 
  to 
  the 
  

   main 
  stem 
  because 
  they 
  are 
  subject 
  to 
  mutual 
  electrostatic 
  

   repulsion. 
  

  

  The 
  organic 
  appearance 
  of 
  the 
  growths. 
  — 
  Though 
  the 
  copper 
  

   and 
  silver 
  growths 
  are 
  very 
  alike 
  they 
  differ 
  materially 
  from 
  

   those 
  derived 
  from 
  iron. 
  They 
  seem 
  characteristic 
  of 
  their 
  

   respective 
  metals 
  rather 
  than 
  of 
  the 
  electric 
  forces 
  involved 
  

   in 
  their 
  production, 
  because 
  they 
  remain 
  true 
  to 
  type 
  whether 
  

   the 
  potential 
  difference 
  be 
  50, 
  100, 
  or 
  200 
  volts. 
  The 
  pro- 
  

   perty 
  which 
  determines 
  these 
  differences 
  is 
  thought 
  to 
  be 
  the 
  

   flexibility 
  of 
  the 
  filaments 
  of 
  the 
  different 
  metals. 
  It 
  is 
  

  

  