﻿On 
  the 
  Photography 
  of 
  Ripples. 
  191 
  

  

  4. 
  The 
  so-called 
  cathode-raj^s 
  and 
  x-rays 
  are 
  given 
  off 
  from 
  

   every 
  element 
  of 
  a 
  continuous 
  conductor 
  at 
  a 
  high 
  stage 
  of 
  

   the 
  vacuum 
  in 
  a 
  Crookes 
  tube, 
  both 
  when 
  this 
  conductor 
  

   constitutes 
  the 
  cathode 
  and 
  when 
  it 
  forms 
  the 
  anode 
  of 
  the 
  

   electrical 
  circuit. 
  The 
  term 
  electric 
  rays, 
  possibly 
  rays 
  of 
  

   polarization, 
  would 
  appear 
  to 
  be 
  more 
  comprehensive 
  than 
  

   the 
  terms 
  cathode-ravs 
  and 
  <2?-ravs. 
  ^ 
  

  

  Jefferson 
  Physical 
  Laboratory, 
  

   Harvard 
  University, 
  Cambridge, 
  U.S. 
  

  

  XX. 
  On 
  the 
  Photography 
  of 
  Hippies. 
  — 
  Second 
  Paper, 
  Is 
  

   By 
  J. 
  H. 
  Vincent, 
  B.Sc, 
  A.R.C.Sc* 
  

   [Plates 
  XX.-XXII.J 
  

  

  IN 
  a 
  former 
  paper 
  f 
  , 
  an 
  apparatus 
  was 
  described 
  by 
  which 
  

   the 
  photographs 
  accompanying 
  the 
  paper 
  were 
  obtained. 
  

   In 
  continuing 
  the 
  photographic 
  method 
  of 
  recording 
  experi- 
  

   ments 
  on 
  ripples, 
  the 
  same 
  principles 
  have 
  been 
  employed. 
  

   That 
  is 
  to 
  say, 
  the 
  light 
  which 
  fell 
  on 
  the 
  mercury 
  surface 
  

   was 
  rendered 
  parallel 
  before 
  incidence, 
  and 
  only 
  that 
  light 
  

   which 
  was 
  reflected 
  in 
  a 
  parallel 
  beam 
  was 
  allowed 
  to 
  fall 
  on 
  

   the 
  sensitive 
  plate. 
  

  

  But 
  in 
  order 
  more 
  faithfully 
  to 
  reproduce 
  the 
  phenomena, 
  

   it 
  appeared 
  that 
  light 
  of 
  practically 
  normal 
  incidence 
  should 
  

   be 
  employed. 
  This 
  was 
  brought 
  about 
  by 
  using 
  only 
  one 
  

   large 
  condensing 
  lens, 
  and 
  by 
  placing 
  the 
  first 
  spark-gap 
  

   (*. 
  e. 
  the 
  one 
  which 
  furnishes 
  the 
  light 
  t 
  o 
  take 
  the 
  photographs) 
  

   close 
  to 
  the 
  brass 
  mounting 
  of 
  the 
  camera 
  lens. 
  The 
  camera 
  

   was 
  thus 
  pointing 
  vertically 
  downwards, 
  and 
  was 
  so 
  placed 
  

   that 
  the 
  vertical 
  projection 
  of 
  the 
  lens-stop 
  and 
  the 
  first 
  

   spark-gap 
  fell 
  equidistant 
  from, 
  and 
  on 
  opposite 
  sides 
  of, 
  the. 
  

   centre 
  of 
  the 
  condensing 
  lens. 
  

  

  The 
  camera 
  lens 
  was 
  provided 
  with 
  an 
  iris 
  diaphragm. 
  

   The 
  stop 
  used 
  was 
  F 
  64 
  except 
  where 
  otherwise 
  stated. 
  

  

  It 
  was 
  found 
  that 
  the 
  time 
  of 
  duration 
  of 
  the 
  spark 
  was 
  not 
  

   unduly 
  increased 
  by 
  the 
  use 
  of 
  magnesium 
  terminals. 
  The 
  

   focal 
  lengths 
  of 
  the 
  front 
  achromatic 
  lens 
  of 
  the 
  camera; 
  

   combination 
  and 
  of 
  the 
  condensing 
  lens 
  were 
  determined 
  for 
  

   blue 
  light, 
  and 
  the 
  large 
  lens 
  w 
  r 
  as 
  placed 
  at 
  a 
  calculated, 
  

   distance 
  from 
  the 
  camera, 
  so 
  that 
  the 
  light 
  from 
  the 
  spark-gap 
  

   was 
  brought 
  to 
  a 
  focus 
  on 
  the 
  centre 
  of 
  the 
  lens-stop. 
  

  

  In 
  selecting 
  a 
  position 
  in 
  the 
  laboratory 
  to 
  set 
  up 
  the 
  

   apparatus 
  the 
  desirable 
  conditions 
  are 
  those 
  of 
  steadiness 
  and 
  

  

  * 
  Communicated 
  bv 
  Prof. 
  J. 
  J. 
  Thomson, 
  F.E.S. 
  

   t 
  Pbil. 
  Mag., 
  June'1897; 
  Proc. 
  of 
  Phys. 
  Sec, 
  July 
  1897. 
  

  

  P2 
  

  

  