﻿ii 
  

  

  20 
  TT. 
  II. 
  Ilohhs 
  — 
  Spiral 
  Falgurite 
  from 
  W{sco?2'n?i. 
  

  

  discharges 
  in 
  a 
  magnetic 
  field, 
  and 
  the 
  lightning 
  discharge. 
  

   Hittorf 
  found 
  that 
  in 
  the 
  case 
  of 
  negative 
  discharge 
  in 
  a 
  direc- 
  

   tion 
  nearly 
  parallel 
  to 
  a 
  line 
  of 
  force 
  that 
  the 
  spark 
  takes 
  the 
  form 
  

   of 
  a 
  dextro-rotary 
  spiral 
  and 
  wraps 
  itself 
  about 
  the 
  line 
  of 
  

   force. 
  It 
  hardly 
  seems 
  possible 
  that 
  the 
  earth's 
  field 
  would 
  be 
  

   sufficiently 
  strong 
  to 
  effect 
  such 
  a 
  change 
  in 
  the 
  course 
  of 
  the 
  

   lightning, 
  and, 
  moreover, 
  the 
  return 
  discharge 
  would 
  be 
  of 
  an 
  

   opposite 
  character, 
  and 
  should 
  produce 
  a 
  spiral 
  of 
  the 
  opposite 
  

   kind 
  unless 
  the 
  initial 
  discharge 
  controls 
  the 
  form 
  of 
  the 
  sand 
  

   tube. 
  The 
  above 
  is, 
  therefore, 
  offered 
  only 
  as 
  a 
  suggestion 
  

   and 
  not 
  in 
  any 
  sense 
  as 
  an 
  adequate 
  explanation. 
  

  

  I 
  do 
  not 
  remember 
  to 
  have 
  seen 
  any 
  description 
  of 
  artificial 
  

   fulgurites. 
  Professor 
  Wood, 
  on 
  being 
  shown 
  the 
  Cutler 
  ful- 
  

   gurite, 
  expressed 
  the 
  belief 
  that 
  he 
  could 
  make 
  some 
  of 
  the 
  

   ordinary 
  kind. 
  Within 
  a 
  half 
  hour 
  he 
  had 
  produced 
  the 
  tubes 
  

   which 
  are 
  shown 
  in 
  fig. 
  2, 
  by 
  immersing 
  carbon 
  electrodes 
  in 
  a 
  

   bath 
  of 
  sand 
  and 
  passing 
  the 
  current 
  from 
  an 
  ordinary 
  arc 
  cir- 
  

   cuit 
  through 
  them. 
  In 
  a 
  of 
  the 
  figure 
  is 
  seen 
  a 
  fulgurite 
  hav- 
  

   ing 
  a 
  hollow 
  protuberance 
  on 
  one 
  side 
  — 
  really 
  a 
  branch 
  of 
  the 
  

   tube 
  ; 
  Z> 
  is 
  a 
  tube 
  of 
  fairly 
  symmetrical 
  cross 
  section 
  ; 
  the 
  tube 
  

   c 
  has 
  a 
  marked 
  corrugation 
  extending 
  along 
  one 
  side, 
  and 
  

   shows 
  perhaps 
  a 
  slight 
  trace 
  of 
  spiral 
  curving 
  ; 
  while 
  d 
  (shown 
  

   in 
  cross 
  section) 
  indicates 
  how 
  large 
  fulgurites 
  may 
  be 
  made 
  

   by 
  this 
  simple 
  method. 
  I 
  am 
  indebted 
  to 
  Professor 
  Wood 
  for 
  

   permission 
  to 
  publish 
  a 
  photograph 
  of 
  these 
  artificial 
  fulgurites. 
  

  

  University 
  of 
  "Wisconsin. 
  

  

  