a86  Papers  relative  to  an  Accident 
on  which  the  light  appeared  was  that  next  to  the  copper 
ball : and  the  general  appearance  of  it  was  round,  and 
fometimes  more  than  half  an  inch  in  diameter.  It 
did  not  fend  forth  rays  or  ftreams  that  were  luminous; 
neither  did  it  extend  beyond  the  furface ; or  the  diftance 
to  which  it  did  extend  was  fo  inconfiderable,  as  to  feem 
incapable  of  being  afcertained,  even  at  the  inftant  before 
the  explofion,  when  it  was  moft  vivid;  though  at  that 
time  there  did  appear  fomething  like  a fmall  fwell 
towards  the  centre,  as  if  it  was  making  an  effort  to  get 
out.  Whenever  the  wheel  was  flopped  fuddenly,  or  the 
motion  of  it  decreafed,  the  light  retired  on  the  inftant, 
and  totally  vanifhed : but  when  the  motion  of  the  wheel 
was  renewed  for  a little  time,  the  light  returned  as  be- 
fore. The  whole  time  that  this  appearance  continued, 
was  never  more  than  five  or  fix  feconds : reckoning  from 
the  moment  it  was  firft  feen,  to  the  inftant  when  the  ex- 
plofion happened.  The  diftance  between  the  point  and 
the  tin  ball  meafured  three  inches  and  a quarter.  There 
was  no  fuch  appearance  on  the  copper  ball ; nor  is  it  eafy 
to  conceive  how  there  ever  fhould,  when  all  the  circum- 
ftances  are  taken  into  confideration. 
exp.  xxxv.  Upon  repeating  this  experiment  with  a 
rounded  end,  inftead  of  a point,  and  at  the  fame  diftance. 
from  the  tin  ball,  notwithftanding  every  other  circum- 
ftance 
