3^6  Mr.  milner  on  the  Communication  of 
u quirere  poflit  velocitatem  corporis  Q_=#;  dico  fore  z= 
“ —j; , et  lx  tempus  quo  corpus  naturaliter  cadit,  per 
“ altitudinem  r dicatur  /,  erit  tempus  infumptum  a cor- 
“ pore  q=  t \j  ‘Pjy-  5 id  quod  experientiae  conforme  efle 
(t  plurimis  inftitutis  experimentis  femper  inveni.” 
Both  thefe  conclxxlions  are  derived  by  this  author  from 
the  principle*  which  they  call  the  confervatio  virium  vJ- 
varum ; but  as  he  has  not  given  us  the  feveral  fteps  of 
his  reafoning,  it  may  be  ufeful  to  fupply  them  here,  be- 
fore we  proceed  to  make  any  i-emarks  upon  his  folution.. 
And  firft,  fuppofe  the  axis  at  D to  be  perpendicular  to  the 
plane  of  the  figure,  and.  conceive  the  whole  body  to  be 
refolved  into  an  indefinite  number  of  prifmatic  particles, 
each  of  which  is  perpendicular  to  the  fame  plane.  Let 
E reprefent  the  fum  of  all  the  particles  multiplied  by 
the  fquares  of  their  refpedlive  diftances  from  the  axis; 
and  e lhall  be  equal  to  vxab,  as  is  demonftrated  by  all 
the  writers  who  treat  of  the  center  of  gyration.  Let  v 
be  the  velocity  which  is  actually  acqxxired  by  Q_after  it  has 
defcended  through  the  fpace  R ; v the  velocity  which  it 
would  have  acquired  by  the  fame  defcent,  provided  the 
body  had  fallen  freely  by  its  gravity;  and  becaufe  the 
vires  viva  are.  incapable  of  diminution  or  increafe,  we 
have 
