Papers  relative  to  an  Accident 
236 
1.  T’be  Report  of  the  Committee  appointed  by  the  Royal 
Society , for  examining  the  Ejfeci  of  Lightning , May  15, 
1777,  on  the  Parapet-wall  of  the  Houfe  of  the  Board  of 
Ordnance , at  Purfleet  in  Eflex. 
THE  iron  cramp  on  which  the  lightning  fell  was 
cemented  into  the  copeing  ftones  on  the  parapet-wall, 
near  the  North-eaft  corner,  with  lead : and  on  that  lead, 
at  one  end  of  the  cramp,  there  appeared  to  have  been  a 
fmall  fufion;  the  end  of  the  lead,  and  part  of  the  adjoin- 
ing ftone,  being  indented  about  half  an  inch  in  diameter, 
and  a quarter  of  an  inch  deep,  as  though  a mufquet-ball 
had  been  fired  againft  them. 
The  iron  cramp  was  fituated  over  a plate  of  lead,  and 
the  ends  of  it,  which  were  inferted  in  the  ftone,  came 
within  feven  inches  of  that  plate,  which  communicated 
with  the  gutter,  and  ferved  as  a fillet  to  it : this  gutter 
was  a part  of  the  main  conductor  of  the  building. 
When  the  lightning  had  quitted  the  iron  cramp,  and 
had  paired  through  feven  inches  of  ftone,  brick,  and 
mortar,  it  fell  upon  the  corner  of  the  plate  of  lead  above- 
mentioned,  as  appeared  by  the  fufion  of  a very  finall 
portion  of  it  difcovered  by  pulling  out  the  bricks,  mor- 
4 tar, 
