from  Lightning  at  Purfleet.  285 
very  well  acquainted  with  this  fubje£l.  However,  I have 
related  it  not  only  as  it  is  a fa£t  of  a very  curious  kind, 
but  as  the  confequences  which  may  be  drawn  from  it 
feem  to  be  confiderable. 
During  the  courfe  of  this  inquiry,  having  occafion  to 
try  fome  experiments  in  the  dark,  I obferved  a curious 
circumftance,  which  feemed  to  fliew,  that  a point  had  a 
far  greater  influence  upon  the  charged  fubftitute,  in  cer- 
tain circumftances,  than  a rounded  end  had  when  it  was 
placed  in  the  fame  lituation. 
exp,  xxxxv.  The  circumftance  alluded  to  was  an  ap- 
pearance of  light  upon  the  brafs  ball  (for  fo  I call  it,  to 
be  more  clear  in  the  defcription)  that  was  fixed  at  the 
end  of  the  great  cylinder,  when  the  copper  ball  (for  fo  I 
call  that  for  the  fame  reafon)  of  the  lefs  fubftitute  was 
oppofed  to  it  at  the  greateft  ftriking  diftance,  as  in  the 
eighteenth  experiment,  every  other  circumftance  re- 
maing  the  fame ; and  whilft  the  model,  with  its  pointed 
conductor,  flood  upon  the  table  diredtly  under  the  tin 
hall  that  was  fixed  at  the  remote  end  of  the  lefs  fubfti- 
tute : for  foon  after  feven  or  eight  turns  of  the  wheel,  a 
light  began  to  appear  on  the  brafs  ball,  and  continued  to 
increafe  in  brightnefs  till  the  moment  it  burft  forth  in  an 
explofion  towards  the  copper  ball.  The  part  of  the  brafs 
O02 
on 
