Mr.  de  luc  on 
45  2 
dulum,  in  order  to  confider  it  in  a point  of  view  ftili 
more  important. 
I now  return  to  the  comparative  dilatations  of  cdafs 
and  brafs;  I mean  to  the  experiments  which  I made 
in  order  to  determine  at  what  heighth  of  the  lamella  of 
brafs  the  point  was,  which  fliould  remain  unmoved  by 
the  variations  of  heat., 
Thefe  experiments,  notwithftanding  all  my  pains,, 
turned  our  furprizingly  irregular;  and  it  was  neceflary 
to  make  a great  number  of  them,  to  arrive  at  any  degree 
of  probability.  In  the  firft  place,  the  duration  of  the 
operations  made  the  brafs  take,  what  I have  named,  the 
habit  of  its  date,  which  prevented  it  from  returning 
exactly  to  that  in.  which  it  was  at  the  fame  degree  of 
heatr 
a cctte  corredlion  c!u.  pcndule,  pour  la  confiderer  faus  une  face  plus  importantc- 
encore. 
Je  reviens  aux  dilatations  comparatives  du  verre  et  du leton;  c’eft  a dire  & 
ces  experiences  par  lefquelies  je  cherchois  a determiner  a quelle  hauteur  fur  la 
lame  de  leton  fe  trouveroit  le  point  qui  refleroit  immobile  par  les  variations  de 
la-  chaleur. 
Malgre  tous  les  foi ns  quc  jo  pris,  ces  experiences -fe  trouverent  d’une  irregu- 
lari teJurpren ante \ et  il  fallut  en  faire.un  bien  grand  nombre  pour  arriver  a des  • 
refultats  un  peu  probables^  'D^abord,  la  longueur  des  operations  faifoit  toujours 
prendre  au  leton  ce  que  j’ai  appell.e  1’habitude  de  fon  etat;  ce  qui  l’empechoit. 
de  revenir  exa&ement  a. celui.au  il  etoit  auparavant  par  ie  raemc  degre  decha- 
leur». 
