364  Mr.  milner  on  the  Communication  of 
pofirion  of  ufeful  machines,  in  which  motions  are  rather 
to  be  preferved  by  the  gradual  effects  of  weights  and 
preffures.  An  accurate  knowledge  therefore  of  thefe 
effects  is  more  effential  to  the  interefts  of  fociety;  and 
the  only  way  of  arriving  at  fuch  a knowledge  is  always 
to  diftinguifh  thofe  principles  which  nobody  denies, 
from  thofe  others  which  are  found  to  take  place  only  in 
fome  particular  circumftances.  The  following  problem 
was  propofed,  and  a folution  given  to  it  long  ago,  by 
D.  BERNOULLI^. 
(g)  Comment,  Petrop.  tom.  IL 
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