306  Papers  relative  to  an  Accident 
two  ends  of  the  wire  within  the  cartridge  may  be  at  a 
proper  diftance  from  each  other;  which  diftance  will 
depend  upon  the  ftrength  of  the  charge.  When  every 
thing  is  thus  adjufted,  and  the  circuit  properly  made,  the 
gun-powder  is  generally  fired;  I fay  generally,  becaufe 
it  fometimes  happens,  that  the  charge  is  not  great  enough 
to  produce  the  effect  required.  For  this  effect  does  not  ap- 
pear to  proceed  from  the  fpark  or  the  explofion  produced 
by  the  fluid  (becaufe  flame  of  a certain  denfity  will  not  fire 
gun- powder);  but  it  muff  be  from  the  ends  of  the  two 
wires,  or  from  one  of  them  at  leaft,  within  the  cartridge, 
being  rendered  hot  enough  to  fire  the  gun-powder,  in 
confequence  of  the  very  great  quantity  of  the  fluid,  and 
the  velocity  with  which  it  paffed  through  the  wire  at  that 
moment:  it  being  well  known  that  wire,  even  of  a con- 
fiderable  thicknefs,  has  been  frequently  made  red-hot, 
and  even  melted,  by  the  Leyden  charge. 
Dr.  lind,  a gentleman  who  is  well  acquainted  with 
this  fubject,  favoured  me  with  a fight  of  a very  curious 
experiment,  which  feems  to  fhew  more  clearly  what  has 
been  advanced  above,  refpe cling  the  immediate  caufe  of 
the  gun-powder’s  taking  fire  in  the  Leyden  experiment. 
He  procured  for  the  purpofe  fome  extraordinary  fine 
threads  or  fhavings  of  fteel;  one  of  which  was  lo  difpofed, 
where  gun-powder  was  properly  lodged  and  confined,  as 
to 
