from  Lightning  at  Purfleet.  277 
appeared  manifeftly  by  the  motion  introduced  in  the 
twenty-fecond  experiment,  where  the  two  fubftitutes 
were  united : for  the  refiftance  at  a point  being  feeble, 
when  in  this  experiment  a point  was  fuddenly  brought 
towards  the  ball  at  the  end  of  the  great  apparatus 
in  charge,  the  whole  of  that  charge  muft  of  confe- 
quence  rufh  towards  the  point  in  an  inftant,  to  difcharge 
itfelf  into  the  earth.  This,  I apprehend,  was  the  true 
reafon  why  we  obtained  an  explofion  at  the  diftance  of 
nine  inches  and  an  half. 
Having  now  gone  through  the  experiments  where 
points  were  introduced,  we  fhall  next  relate  the  feveral 
experiments  where  other  terminations  were  ufed.  By 
this  method  of  proceeding,  we  fhall  be  able  to  form  a 
proper  judgement  what  kind  of  conductors  are  the  moll 
advantageous  for  fecuring  buildings,  &c. 
exp.  xxiii.  On  repeating  the  eighteenth  experiment, 
but  with  a rounded  conduit  or  upon  the  model,  every 
other  circumftance  continuing  the  fame,  and  the  model 
at  reft,  the  greateft  diftance  at  which  it  was  ftruck  (in 
confequence  of  ten  or  eleven  turns)  was  not  more  than 
three  quarters  of  an  inch. 
Now  if  we  compare  this  diftance  with  that  at  which 
the  point  was  ftruck  in  the  eighteenth  experiment,  the 
proportion  will  be  found  to  be  lefs  than  one  to  five. 
N n 2 
But 
