Motion  by  Impact  and  Gravity*.  361 
extremely  fimple,  eafy  to  be  defcribed ; and  I do  not  find 
that  it  has  ever  been  anfwered  by  any  of  the  advocates 
for  the  new  doctrine  of  forces. 
“ Let  a and  b be  two  equal 
“ bodies  that  are  feparatecl  from 
“ each  other  by  fprings  inter- 
u pofed  between  them,  in  a 
“ fpace  efgh,  which  in  the  ® 
“ mean  time  proceeds  uniformly  in  the  direction  ba  (in 
“ which  line  the  fprings  att)  with  a velocity  as  1 ; and 
“ fuppofe  that  the  fprings  imprefs  on  the  equal  bodies  a 
“ and  b equal  velocities,  in  oppofite  directions,  that  are. 
u each  as  1.  Then  the  abfolute  velocity  of  a (which, 
u was  as  1)  will  now  be  as  a ; and  according  to  the  new 
“ doCtrine  its  force  as  4:  whereas  the  abfolute  velocity 
u and  force  of  b (which  was  as  1)  will  now  be  deftroyed; 
“ fo  that  the  aCtion  of  the  fprings  adds  to  a a force  as  3,, 
“ and  fubduCts  from  the  equal  body  s a forte  as  one 
“ only ; and  yet  it  feems  manifeft,  that  the  actions  of  the 
w fprings  on  thefe  equal  bodies  ought  to  be  equal,  and 
u M.  Ber  noulli  exprefsly  owns  them  to  be  fo (c>.  I flaalL 
only  juft  obferve,  that  if  M.  Bernoulli  exprefsly  owns,, 
that  fprings,  interpofed  between  two  bodies  in  a fpace,, 
which  is  carried  uniformly  in  the  direction  in  which  the 
I ' 
- (e)  Book  II.  chap.  2.  Account  of  newton’s  difcoveries. 
fprings 
