3 6o  Mr.  Milner  on  the  Communication  of 
perfectly  hard,  and  letting  fall  the  perpendicular  rs;  cs 
will  be  the  velocity  acquired  by  a in  that  cafe ; and,  uni- 
verfally,  the  velocity  acquired  by  a will  be  equal  to 
C S 
c s+— , if  the  elafticity  of  the  bodies  be  to  perfect  elafticity 
as  i : m.  In  order  to  determine,  therefore,  when  cn+CL 
can  poflibly  be  equal  to  cr+  — , or,  which  is  the  lame 
thing,  l s + c n equal  to  — , we  are  to  confider  that  ns:~Ls:'. 
i :m:  andbecaufec«  is  equal  to  cs-sn,  cn=cs-^jj> 
and  it  is  obvious  that  cs  + ls-~  can  never  be  equal  to 
c y 
— , unlefs  m be  taken  equal  to  unity,  and  Bernoulli’s 
hypothelis  is  plainly  impoflible  in  all  cafes  where  the 
bodies  are  not  fuppofed  perfectly  elaftic. 
But  though  we  confefs  the  learned  author,  who  firft 
folved  the  problem  we  have  been  conlidering,  deferves 
no  commendation  for  propofing  in  a general  form  what 
ought  to  have  been  reftrained  to  a particular  cafe,  yet  it 
will  by  no  means  follow,  that  every  argument  which  has 
been  advanced  againft  this  doctrine  is  either  intelligible 
or  fatisfactory.  Of  all  the  objections  and  experiments 
which  have  been  ftarted  and  contrived  to  refute  the 
new  opinions  of  the  German  philofophers,  there  is  none 
which  carries  a greater  degree  of  plaulibility  along  with 
it,  than  a celebrated  invention  of  Mr.  m aclaurin.  It  is 
-extremely 
