from  Lightning  at  Purfleet.  251 
that  was  propofed  to  draw  the  model,  and  the  lefler 
another  line  fufpending  two  weights  which  regulated 
its  motion.  For  after  the  heavier  weight  had  defcended 
fo  far  as  to  bring  the  model  direftly  under  the  fubftitute, 
it  was  then  checked ; but  the  leiTer  weight  continuing  to 
defcend,  the  model  moved  forward  with  its  acquired  ve- 
locity, joined  to  the  power  of  the  leiTer  weight.  And 
that  the  remaining  motion  might  at  laft  be  overcome, 
without  ftriking  againft  the  two  polls,  fome  narrow  flips 
of  cloth  feven  feet  long,  were  nailed  upon  the  frame, 
in  thofe  parts  over  which  the  model  Was  to  pafs  be- 
fore it  reached  the  end.  This  model  moved  like  a fledge, 
by  means  of  two  flips  of  wood  that  were  fixed  at  the 
bottom,  which  ran  in  two  grooves  that  were  cut  along 
the  frame  from  end  to  end.  And  the  line  which  drew 
the  model  along,  was  fixed  very  near  the  center  of  re- 
finance. 
To  conftrudt  the  fubftitute  for  a cloud,  I firft  joined 
together,  in  fifteen  lengths,  the  broad  rims  of  one  hun- 
dred and  twenty  drums  (merely  to  have  them  portable) 
by  means  of  wood  cut  into  long  flips,  which  were  fixed 
on  the  infides  thereof : but,  as  thofe  drums  were  not  accu- 
rately of  a fize,  the  feveral  joinings  were  covered  over  with 
cloth,  and  pafted  down,  to  make  the  furfaee  throughout 
more  even.  After  this,  the  whole  number  were  properly 
Vol.  LXV1II.  K k covered 
