﻿W. 
  H. 
  Hobhs 
  — 
  Spiral 
  Fulgurite 
  from 
  Wisconsin. 
  19 
  

  

  which 
  shows 
  any 
  approach 
  to 
  this 
  shape 
  is 
  that 
  from 
  Water- 
  

   ville, 
  Maine, 
  described 
  by 
  Bayley,"^ 
  which 
  has 
  marked 
  corruga- 
  

   tions 
  that 
  wind 
  about 
  the 
  axis 
  of 
  the 
  fulgurite 
  in 
  the 
  form 
  of 
  a 
  

   dextro-rotary 
  helix. 
  

  

  The 
  fact 
  that 
  the 
  Waterville 
  and 
  Cutler 
  fulgurites 
  show 
  each 
  

   a 
  spiral 
  twist 
  of 
  the 
  same 
  type 
  is 
  sufficient 
  evidence 
  that 
  the 
  

  

  Fig. 
  2. 
  Artificial 
  fulgurites 
  made 
  by 
  Prof. 
  Wood. 
  The 
  units 
  iu 
  the 
  scale 
  are 
  

   inches, 
  a 
  is 
  a 
  tube 
  with 
  branch-like 
  protuberance 
  at 
  the 
  side. 
  & 
  is 
  a 
  tube 
  of 
  

   nearly 
  symmetrical 
  cross-section, 
  c 
  is 
  a 
  tube 
  "vvith 
  marked 
  corrugation 
  extending 
  

   along 
  one 
  side, 
  d 
  exhibits 
  the 
  cross-section 
  of 
  a 
  large 
  tube. 
  

  

  structure 
  is 
  not 
  an 
  accidental 
  one, 
  but 
  one 
  to 
  be 
  explained 
  by 
  

   the 
  conditions 
  of 
  the 
  lightning 
  discharge, 
  which 
  doubtless 
  fol- 
  

   lowed 
  a 
  spiral 
  course 
  through 
  the 
  sand. 
  Professor 
  R. 
  W. 
  

   Wood, 
  of 
  the 
  Physical 
  Department 
  of 
  the 
  University 
  of 
  Wis- 
  

   consin, 
  has 
  suggested 
  to 
  me 
  that 
  this 
  may 
  be 
  explained 
  in 
  some 
  

   way 
  by 
  the 
  influence 
  of 
  the 
  earth's 
  magnetic 
  Held 
  upon 
  the 
  

   discharge. 
  There 
  is 
  at 
  least 
  a 
  possibility 
  that 
  there 
  may 
  be 
  

   some 
  analogy 
  between 
  the 
  experiments 
  of 
  Hittorff 
  with 
  electric 
  

  

  * 
  A 
  Fulgurite 
  from 
  Waterville, 
  Maine, 
  by 
  W. 
  S. 
  Bayley, 
  this 
  Journal 
  (3), 
  1892, 
  

   xliii, 
  p. 
  327. 
  

  

  t 
  J. 
  J. 
  Thomson, 
  Recent 
  Researches 
  iu 
  Electricity 
  and 
  Magnetism. 
  Oxford, 
  

   1893, 
  p. 
  134. 
  

  

  