Pyrometry  and  Jreometry , See. 
469 
Effay  upon  the  rneafure  of  the  ahfolute  expanfion  of  bodies 
by  heat . 
Though  I did  not  at  firft  intend  to  make  ufe  of  my  in- 
ftrument  in  the  meafure  of  ahfolute  expanfions,  I could 
not  help  making  fome  experiments  on  this  fubjedt. 
Befides  the  immoveable  wire  placed  in  the  focus  of 
the  Microfcope,  I had  defired  Mr.  ramsden  to  put  in 
another,  moveable  by  a ferew:  I then  began,  firft,,  by 
feeking  the  value  of  the  parts  of  the  Micrometer,  in 
doing  which  the  little  fcale  I had  traced  on  the  lamella 
of  brafs  was  again  of  fervice  to  me.  I had  made  it  as 
exadl  as  I poffibly  could;  each  of  its  divifions  was  the 
400th  part  of  a French  foot.  The  divided  part  of  it  was 
three 
Effai  fur  la  me  furs  des  expanfions  abfolues  des  corps  par  la  chaleur . 
Quoique  je  n’euffe  pas  intention  d’abord  d’employer  ma  machine  a mefurer  des 
expanlions  abfolues,  jene  laiffai  pas  de  tenter  quelques  experiences  fur  cetobjet. 
Outre  le  fil  immobile  place  au  foyer  du  Microfcope,  j’avois  demande  a Mr 
ramsden  d’en  mettre  un  qui  fut  mobile,  et  conduit  par  une  vis.  Je  cherchai 
done  d’abord  la  valeur  des  parties  du  Micrometre;  a quoi  me  fervit  encore  la 
petite  echelle  tracee  fur  ma  lame  de  leton.  Je  Tavois  faite  aufli  exa&ement  qu’il 
m’avoit  ete  poflible,  et  fes  parties  etoient  des  400mes  du  pied  de  France.  File 
avoit 
