Mr.  de  luc  on 
470 
three  French  inches  in  length,  confequently  confifted  of 
100  of  thefe  parts,  that  were,  or  were  fuppofed  to  be, 
equal. 
Pointing  then  my  Microfcope  at  fir  ft  upon  one  of  the 
extremities  of  the  fcale,  the  two  wires  coinciding,  I 
brought  the  moveable  wire  to  the  next  point,  counting 
the  turns  of  the  fcrew : then  conducting  the  immoveable 
wire  from  one  part  to  another  of  the  fcale,  and  bringing 
at  every  change  the  moveable  wire  to  the  point  imme- 
diately following,  I noted  all  thefe  lengths  of  the  parts 
meafured  by  the  Micrometer,  the  fmall  differences  of 
which  marked  the  imperfections  of  the  fcale.  The  mean 
of  thefe  100  meafures  gave  me  21,333  turns  of  the 
fcrew,  for  a part  of  my  fcale,  that  is,  for  jt_th  of  a 
French  foot.  This,  according  to  the  proportion  of  1 6 to 
1 5 between  this  foot  and  the  Englifh,  a proportion  exaCt 
enough 
avoit  3 pouces  de  France  dans  la  portion  divifee,  et  par  confequent  ioo  de  ces 
parties  egales,  oucenfees  Petre. 
Pointant  done  d’abord  mon  Microfcope  fur  Pune  des  extremites  de  Pechelle, 
tandis  que  les  deux  fils  coincidoient,  j’amenai  le  fil  mobile  fur  le  point  fuivant, 
en  comptant  les  tours  de  la  vis;  puis  conduifant  le  fil  immobile  de  partie  en  partie 
de  l’echelle,  et  amenant  a chaque  fois  le  fil  mobile  au  point  immediatement  fui- 
Vant,  je  notai  toutes  ces  grandeurs  des  parties,  mefurees  par  le  Micrometre,  dont 
les  petites  differences  marquoient  les  imperfeftions  de  Pechelle.  Le  milieu  entre 
ces  100  melures  me  donna  2 1,333  tours  de  la  vis,  pour  une  partie  de  mon  echelle, 
e’en  a dire  pour  4^0  du  pied  de  France.  Ce  qui,  dans  le  rapport  de  16  a 15  de  ce 
pied 
