Mr.  button  on  the  initial 
54 
thofe  of  two  or  three  feet  only  ; which  fmall  velocity 
being  meafured  by  any  convenient  means,  let  the  num- 
ber denoting  it  be  increafed  in  the  proportion  of  the 
weight  of  the  ball  to  the  weight  of  the  ball  and  block 
together,  and  the  original  velocity  of  the  ball  itfelf  will 
thereby  be  obtained.  In  thefe  experiments,  this  reduced 
velocity  is  rendered  very  eafy  to  be  meafured  by  a very 
Ample  and  curious  contrivance,  which  is  this : the  block 
of  wood,  which  is  ftruck  by  the  ball,  is  not  left  at  li- 
berty to  move  ftraight  forward  in  the  direction  of  the 
motion  of  the  ball,  but  it  is  fufperided,  as  the  weight  or 
bob  of  a pendulum,  by  a ftrong  iron  ftem,  having  a 
horizontal  axis  at  top,  on  the  ends  of  which  it  v orates 
freely  when  ftruck  by  the  ball.  The  eonfequence  of 
this  Ample  contrivance  is  evident:  This  large  balliftic 
pendulum,  after  being  ftruck  by  the  ball,  will  be  pene- 
trated by  it  to  a fmall  depth,  and  it  will  then  fwing  round 
its  axis  and  defcribe  an  arch,  which  will  be  greater  or 
lefs  according  to  the  force  of  the  blow  ftruck ; and  from 
the  fize  of  the  arch  defcribed  by  the  vibrating  pendu- 
lum, the  velocity  of  any  point  of  the  pendulum  itfelf 
can  be  eafily  computed;  for  a body  acquires  the  fame 
velocity  by  falling  from  the  fame  height,  whether  it  de- 
fcend  perpendicularly  down,  or  otherwife ; therefore,  the 
length  of  the  arch  defcribed,  and  of  its  radius,  being 
5 given, 
