Motion  by  ImpaB  and  Gravity . 347 
But  a new  opinion  Was  now  flatted  by  M.  Leibnitz 
concerning  the  forces  of  bodies  in  motion.  The  force  of 
a body  in  motion  and  its  momentum  had  hitherto  been 
cbnfidered  as  fynonymous  terms,  and  had  alike  been  mea- 
sured by  the  quantity  of  matter  and  velocity  conjointly. 
On  the  contrary,  leibnitz  and  his  followers  affirmed, 
that  the  force  was  proportional  to  the  quantity  of  matter 
in  the  moving  body  and  the  fquare  of  its  velocity.  It  is 
needlefs  to  relate  all  that  paffed  on  both  fides : fo  ma- 
terial an  oppofition  in  fentiment  neceflarily  produced 
Very  warm  contention  ; and,  as  it  generally  happens  in 
■other  difputes,  we  do  not  hear  of  any  conviction  being 
produced  on  either  fide. 
After  furveying  the  arguments  of  the  difputants,  it  is 
not  eafy  to  fay,  whether  the  agitation  of  the  queflion 
before  us  has  contributed  to  retard  or  advance  the  pro- 
grefs  of  truth  and  fcience.  Gn  the  one  hand,  many  in- 
genious experiments  have  been  made,  many  curious  pro- 
blems invented  and  refolved,  which  probably  would 
never  onch  have  been  thought  of  by  men  who  were  in 
the  purfuit  of  truth  in  a more  cool  and  deliberate  way : 
and,  on  the  other  hand,  it  may  juftly  be  affirmed,  that 
the  violence  of  prejudice  and  party-fpirit  has  fo  much 
clouded  the  reafonings  of  the  belt  writers,  that  we  fenli- 
bly  feel  their  influence  to  this  day.  I need  not  diflemble : 
Vol.  LXVIIh  Y y it 
