25°  Papers  relative  to  an  Accident 
compared  with  the  houfe,  was  one- third  of  an  inch  to  a 
foot. 
In  regard  to  the  wood  of  which  the  model  was  made, 
I took  care  that  it  was  well  baked,  and  foaked,  whilft  hot, 
in  drying  oil,  before  the  feveral  parts  were  joined  toge- 
ther, that  it  might  be  the  more  fimilar  to  the  bricks  and 
other  materials  of  the  building  itfelf,  in  the  power  of  re- 
filling the  paflage  of  the  fluid,  whenever  any  attack 
thereof  fhould  be  made.  For  brick,  Hone,  dry  lime,  8cc. 
had  been  obferved  many  years  ago  by  Mr.  delaval  and 
others  to  refill  the  paflage  of  this  fluid  very  conli- 
derably. 
In  order  to  move  this  model  with  the  velocity  re- 
quired, it  was  necefiary  to  have  a frame  of  wood,  of  fuch 
a length  as  would  fuller  the  model,  with  the  pointed 
conductor  upon  it,  to  be  out  of  the  reach  or  influence 
of  the  charge  contained  in  the  cylinder,  both  at  its  fet- 
ting  off,  and  when  it  had  arrived  at  the  end  of  its 
journey. 
To  this  frame,  two  upright  polls  of  wood,  ten  feti 
and  a half  long,  were  fixed  at  the  farther  end,  and  a'  a 
dillance  from  each  other  equal  to  the  width  of  the 
frame.  Upon  the  top  of  thefe  polls,  and  in  the  middle 
between  them,  were  fixed  two  wheels  of  different  dia- 
meters upon  the  fame  axis.  The  larger  took  the  line 
7 
that 
