57 6 Mr.  milner  on  the  Communication  of 
the. fame  both  in  the  firft  and  fecond  experiment,  it  fol- 
lows, that  the  forces  are  very  nearly  to  one  another  as 
a'p  to  , or  as  4 to  i : and  in  the  lame  way  the  other 
experiments  are  fhewn  to  be  confident  with  the  theory. 
1 chofe  to  premife  a fhort  account  of  the  opinions  which 
the  philofophers  before  Galileo  entertained  concerning 
the  motions  of  bodies;  becaufe  their  mi  flake  n ideas  of 
theeffedls  of  gravity  are  analogous  to  fome  opinions  of 
a later  date,  which  indeed  fuggefted  the  neceffity  of  re- 
suming thefe  inquiries. 
And  as  nothing  in  controverfial  matters  lb  com- 
pletely fatisfies  the  mind  as  an  ex  aft  knowledge  of 
that  particular  which  produces  the  difpute;  I have 
fhewn,  that  the  terms  made  ufe  of  to  exprefs  the  third 
law'  of  motion  were  taken  in  two  very  different  fenfes : 
that  Sir  Isaac  newton’s  explication  of  them  is  at  bell 
ambiguous,  and  maclaurin’s  abfolutely  falle. 
1 ft.  In  the  demonllration  of  the  firil  cafe  we  fee  that 
the  affertion  of  leibnitz  is  true  in  one  particular  in- 
llance.  When  two  elaftic  balls  move  in  the  fame  llraight 
line,  the  fum  of  their  forces  is  not  altered  by  collilion; 
and  it  is  more  than  probable,  that  this  lingle  circum- 
ftance  was  the  caufe  of  affixing  new  ideas  to  the  terms 
action  and  re-a£tion.  For, 
ad.  In 
