Pyrometry  and  Areometry , See.  435 
common  Barometers;  that  which  I ufed  for  the  frame  of 
my  Hygrometer,  and  on  which  I made  the  experiment, 
had  an  external  diameter  of  about  three-eighths,  and  an 
internal  of  about  one-eighth  of  an  inch : the  rod  was  from 
twenty-one  to  twenty-two  inches  long,  but  it  palled  under 
the  cork  only  eighteen  Englifh  inches,  reckoning  from  the 
point  to  which  was  fixed  at  its  bottom  the  lamella  of  brafs 
the  dilatation  of  which  I wanted  to  compare  with  that  of 
theglafs.  The  lamella  was  applied  from  this  point  length- 
ways and  upwards  along  the  tube : it  had  been  made  thin- 
by  rollers,  to  render  it  the  more  elaftic;  and  as  it  was  too 
thin  to  fupport  itfelf  upright,  I kept  it  ftretched  in 
that  direction  by  means  of  a thread,  which,  going  over 
a pulley,  bore  at  its  other  end  a weight  fit  to  give  it 
the  fame  degree  of  tenfion  which  it  has  in  my  Hygrome- 
ter. 
Upon 
tubes  dont  je  fais  ufage  pour  la  monture  de  mes  Hygrometres,  et  que  je  foumis  a 
l’experience,  ont  environ  f de  pouce  de  diametre  exterieur,  et  d?-|  a l’interieur. 
Le  tube  que  j’emploiai  avoit  21  a 22  pouces  de  long,  mais  il  n’excedoit  le  liege 
que  de  18  pouces  Anglois,  a compter  do  point  ou  etoit  fixeedans  le  bas  la  lame  de 
leton  dont  je  voulois  comparer  la  dilatation  avec  celle  du  verre.  De  ce  point,  la 
lamede  leton  s’elevoit  le  long  du  tube.  Elle  etoit  faite  au  laminoir  pour  la  rendre 
plus  elaftique;  etcomme  elle  fe  trouvoit  trop  mince  pour  fe  foutenir  de  bout  par 
eile-meme,  je  la  tenois  tendue  dans  cette  direction  par  un  fil,  qui,  palTant  fur 
une  poulie,  portoit  a fon  autre  bout  un  poids  propre  a lui  donner  le  merae  degre  dc 
lention  qu’elle  eprouve  dans  mon  Hygrometre, 
F f f 2 
J’avois 
