27.2  Papers  relative  to  an  Accident 
life  fide  of  the  model.  This  wire  was  intended  to  anfwer 
the  purpofe  of  a fpout  in  the  building  at  Purfleet  towards 
■the  South. 
Befides  thefe  precautions,  there  remained  another  cir- 
cumftance  to  be  attended  to,  refpedling  motion : for  fe- 
veral  gentlemen  had  obferved,  that  clouds  in  a thunder- 
ftorm  are  not  always  in  motion;  or  at  leaf!  not  in  the  de- 
gree of  motion  which  has  been  reprefented  in  the  pre- 
ceding experiment.  To  obviate  that  objection,  I propofed 
to  repeat  thofe  experiments  when  the  model  was  at  reft. 
In  order to  prepare  the  whole  apparatus  in  the  moft  pro- 
per manner  for  this  purpofe,  it  was  neceftary  to  attend  to 
the  circumftances  that  are  obferved  in  nature. 
•For  when  a cloud  comes  ready  charged,  and  ftrilces 
another  cloud  with  the  matter  of  lightning,  there  muft 
be  a certain  diftance  at  which  that  effedt  muft  take  place ; 
and  this  we  therefore  call  the  greateft,  or  the  ftriking 
diftance.  Now,  to  produce  fimilar  effects,  our  artificial 
apparatus  muft  confift  of  two  parts  at  leaft,  to  reprefent 
fuch  clouds : and  thofe  parts  muft  be  fo  difpofed  as  not 
to  exceed  the  greateft  diftance  at  which  they  will  ftrike, 
when  the  largeft  part,  or  fubftitute,  is  properly  charged: 
nor  muft  the  diftance  between  them  be  lefs,  for  reafons 
that  will  appear  prefently.  And  therefore,  to  make  the 
(experiment  correfpond  with  nature,  it  will  require  fome 
trouble 
