Pyrometry  and  Areometry , &c. 
543 
I fhall  now  collect  the  refults  of  the  preceding  re- 
flexions with  regard  to  phyfical  meafures. 
When  the  inquiry  is  into  general  caufes,  fuch  as  heat, 
the  eledtric  fluid,  humor , light,  the  weight  of  the  air, 
the  fall  of  bodies,  percuflion,  &c.  caufes  concerning 
which  we  never  acquire  fuflicient  light,  we  muft  endea- 
vour to  find  out  what  are  their  moft  Ample  effects,  in 
order  to  meafure  the  intenfity  of  them  by  thofe 
effects.  In  that  cafe  it  is  proper  that  the  fixed  terms 
of  the  meafure  be  taken  at  the  greateft  poflible 
diftances.  For  it  being  the  moft  Ample  effedt,  and  con- 
fequently  that  which  approaches  neareft  to  follow,  by 
its  degrees,  thofe  of  the  intenfity  of  the  caufe,  it  will 
ferve  as  a common  meafure  for  all  the  other  effedls  de- 
pendant on  it.  One  muft,  therefore,  afcertain  the  uni- 
form 
Je  vais  maintenant  raffembler  ici  les  refultats  des  reflexions  precedentes  a 
Fegard  des  Mefures  phyfiques, 
Lorfqu’il  s’agira  de  caufes  generates,  eomme  la  chaleur,  le  fluide  eledlrique, 
Yhumor , la  lumiere,  le  poids  de  Pair,  la  chute  des  corps,  les  chocs,  &c.  caufes 
fur  l’a£tion  defquelles  nous  n’acquerrons  jamais  aflez  de  lumieres,  il  faut 
chercher  quels  font  leurs  effets  les  plus  fimples,  afin  de  mefurer  leur  intenfite 
par  ces  effets.  Alors  fans  doute  il  convient  que  les  termes  fixes  de  la  mefure 
foyent  pris  aux  plus  grandes  diftances  poflibles.  Car  s'agiffant  de  1’effet  le  plus 
fimple,  et  par  confequent  le  plus  approchant  de  fuivre  par  fes  degres  ceux  de 
1’intenfite  de  la  caufe,  il  fervira  de  mefure  commune  pour  tons  les  autres  effet 
qui  en  dependront.  Il  faut  done  affurer  la  conftru&ion  uniforms  de  la  mefure ; 
ce 
