484  Mr.  de  luc  on 
to  inveftigate  caufes  through  their  effects,  by  meafuring 
thefe  wherever  nature  gives  us  a fufficient  hold,  in  order 
•not  to  he  deceived  by  femblances  of  truth. 
The  firft  rays  of  this  light,  the  dawn  of  all  true  know- 
ledge in  philofophy,  were  extremely  weak.  At  firft 
philofophers  were  fatisfied  with  having  inftruments 
which  indicated  the  exiftence  of  certain  caufes  that  our 
organs  could  either  not  difcover  at  all,  or  difcovered 
very  imperfectly.  Hence  the  modeft  names  given  by  the 
firft  inventors  to  their  inftruments.  They  called  only 
Barofcopes,  Thermofcopes,  Microfcopes,  thofe  inftru- 
ments which  were  intended  to  fhow  the  weight  of  the 
air,  the  dilatation  of  bodies  by  heat,  the  objects  which, 
efcaped  the  naked  eye.. 
Thefe 
en  mefurant  ceux-ci,  partout  ou  la  nature  nousdonne  quelque  prife,  pour  n’etre- 
pas  trompes  par  des  appergus* 
Les  premiers  rayons  de  cette  lumiere,  qui  etoient  Faurore  des  vrayes  connoif- 
fances  en  phylique, . furent  d’abord  tres  foibles.  On  fe  trouva  bien  content 
d’avoir  des  machines  qui  Meat  appercevoir  furement  l’exiftcnce  de  certaines 
caufes,  que  nos  organes  feuls  ne  pouvoient  decouvrir,  ou  ne  decouvroient  quc 
tres  imparfaitement.  De  la  les  denominations  modeftes  que  les  premiers  inven- 
teurs  donnerent  a leurs  machines.  Ils  n’appellerent  que  Barofcopes,  Thermo- 
fcopes, Microfcopes,  leurs  inftrumens  deftines  a montrer,  le  poids  de  Pair,  la 
dilatation  des  corps  par  la  chaleur,  lesobjets  qui  echappenta  la  yue. 
7 On 
