356  iW>\  milner  on  the  Communication  of 
convenient  fuch  modes  of  expreffion  may  appear.  Ee- 
caufe  hoC  + b/32  is  equal  to  a<z2  + b£%  it  is  true  that  no  force 
is  loft  by  a but  what  is  communicated  to  b ; but  not  in 
the  fame  fenfe  in  which  it  was  affirmed  that  no  motion 
is  loft  by  a but  what  is  communicated  to  b.  In  that  cafe 
the  fquares  of  their  abfolute  velocities  are  underftood;  in 
this,  their  velocities  reduced  to  the  fame  direction.  How- 
ever, no  material  ill  confequence  can  poffibly  arife  from 
fuch  a notion  of  adtion  and  re-adtion,  as  long  as  the  quef- 
tion  is  fuppofed  to  concern  only  elaftic  bodies : but  real 
mifchief  is  done,  and  the  debate  ceafes  to  be  verbal, 
whenever  the  law  of  the  equality  of  adtion  and  re-adtion 
is  faid  to  take  place  in  the  collilions  of  all  forts  of 
bodies. 
case  the  second.  But  the  truth  of  thefe  remarks,, 
and  the  neceffity  of  attending  to  the  precife  ufe  of  terms, 
will  appear  in  a ftill  ftronger  light,  if  we  conlider  the  fo- 
lution  of  a problem  given  us  by  j.  Bernoulli 
Suppofe  that  two  equal  and  fpherical  bodies,  a and  b, 
ftruck  at  once  in  the  dirediion  cd  perpendicular  to  the 
line  joining  the  centers  of  a and  b with  a velocity  repre- 
fented  by  a.  Let  the  quantity  of  matter  in  c be  called 
and  the  quantity  of  matter  in  a or  b,  n : let  the  velo- 
(d)  Difcours  fur  le  raouvement. 
city 
6 
