﻿378 
  ON 
  THE 
  CAUSES 
  OF 
  

  

  suredly 
  not 
  unreasonable 
  to 
  ascribe 
  to 
  the 
  analogous 
  electrical 
  appara- 
  

   tus 
  of 
  nature, 
  aided 
  by 
  the 
  elasticity 
  of 
  the 
  air, 
  a 
  vertical 
  hurricane. 
  

   It 
  was 
  under 
  the 
  well 
  founded 
  impression 
  that 
  lightning 
  may 
  be 
  super- 
  

   seded 
  by 
  a 
  current, 
  that 
  we 
  have 
  been 
  instructed 
  by 
  Franklin, 
  to 
  

   surmount 
  our 
  lightning 
  rods 
  by 
  metallic 
  points, 
  by 
  which 
  electrical 
  

   discharges 
  from 
  thunder 
  clouds 
  are 
  expected 
  to 
  be 
  conveyed 
  to 
  the 
  

   earth 
  gradually, 
  which 
  might 
  otherwise 
  pass 
  in 
  sparks 
  of 
  lightning 
  of 
  

   a 
  formidable 
  magnitude. 
  

  

  If, 
  then, 
  it 
  be 
  demonstrated 
  that 
  a 
  continuous 
  discharge 
  of 
  electricity 
  

   may 
  become 
  the 
  substitute 
  for 
  lightning, 
  and 
  that 
  within 
  the 
  sphere 
  of 
  

   the 
  discharge 
  the 
  air 
  may 
  be 
  so 
  lifted 
  as 
  to 
  counteract 
  its 
  gravity; 
  it 
  is 
  

   in 
  the 
  next 
  place 
  only 
  necessary 
  to 
  advert 
  to 
  facts 
  perfectly 
  well 
  known, 
  

   in 
  order 
  to 
  point 
  out 
  a 
  cause 
  of 
  acceleration 
  sufficient 
  to 
  account 
  for 
  

   the 
  well 
  known 
  violence 
  of 
  the 
  tornado. 
  

  

  At 
  the 
  height 
  of 
  fifteen 
  miles, 
  the 
  air 
  has 
  been 
  ascertained 
  to 
  have 
  

   less 
  than 
  one-thirtieth 
  of 
  the 
  density 
  of 
  the 
  stratum 
  next 
  the 
  earth. 
  

   Of 
  course 
  this 
  substratum 
  would 
  exercise 
  a 
  force 
  nearly 
  equal 
  to 
  the 
  

   atmospheric 
  pressure, 
  or 
  about 
  fourteen 
  and 
  a 
  half 
  pounds 
  to 
  the 
  square 
  

   inch, 
  in 
  order 
  to 
  attain 
  the 
  space 
  occupied 
  by 
  the 
  rare 
  medium, 
  to 
  

   which 
  allusion 
  has 
  been 
  made. 
  It 
  follows 
  that 
  if 
  the 
  weight 
  of 
  the 
  

   superincumbent 
  air 
  were 
  removed 
  or 
  counteracted, 
  that 
  the 
  inferior 
  

   stratum 
  would 
  rise 
  with 
  explosive 
  violence. 
  

  

  While 
  the 
  air 
  is 
  thus 
  carried 
  upwards 
  by 
  the 
  concurrent 
  influence 
  

   of 
  electrical 
  attraction, 
  and 
  the 
  reaction 
  of 
  its 
  own 
  previously 
  con- 
  

   strained 
  elasticity 
  ; 
  other 
  bodies 
  are 
  lifted, 
  both 
  by 
  electrical 
  attraction, 
  

   and 
  the 
  blast 
  of 
  air 
  to 
  which 
  it 
  gives 
  rise. 
  Hence 
  houses 
  within 
  the 
  

   sphere 
  of 
  the 
  excitement 
  are 
  burst 
  by 
  the 
  expansion 
  of 
  the 
  air 
  which 
  

   they 
  contain, 
  their 
  walls 
  being 
  thrown 
  outwards, 
  and 
  their 
  roofs 
  car- 
  

   ried 
  away 
  ; 
  while, 
  by 
  the 
  afflux 
  of 
  the 
  atmosphere 
  requisite 
  to 
  the 
  res- 
  

   toration 
  of 
  its 
  equilibrium, 
  trees, 
  houses 
  and 
  other 
  bodies 
  are 
  thrown 
  

   inwards 
  towards 
  the 
  vertical 
  current, 
  from 
  before, 
  as 
  well 
  as 
  from 
  either 
  

   side. 
  

  

  When 
  once 
  a 
  vertical 
  current 
  is 
  established, 
  and 
  a 
  vortex 
  pro- 
  

   duced, 
  I 
  conceive 
  that 
  it 
  may 
  continue 
  after 
  the 
  exciting 
  cause 
  may 
  

   have 
  ceased 
  to 
  act. 
  The 
  effect 
  of 
  a 
  vortex 
  in 
  protecting 
  the 
  space 
  

  

  