460  Mr.  de  luc  on 
experiments,  by  means  of  a fmall  opaque  body  float- 
ing at  the  top  of  them,  and  to  which  the  Microfcope 
may  be  pointed.  I do  not,  however,  infill  upon  this  ap- 
plication of  the  machine;  fince  the  expanfion  of  li- 
quids may  be  obferved  in  vafes,  the  dimenfions  of  which 
are  known,  by  joining  cylindrical  tubes  to  them,  which 
render  their  expanfions  much  more  fenfible.  I fliall  only 
obferve,  that  from  the  knowledge  of  the  dilatability  of  the 
tube,  one  fliould  not  reduce  its  capacity  to  what  it  would  be 
if  the  glafs  did  not  dilate  itfelf,  as  is  done  with  refpedl  to 
vafes  in  order  to  know  the  true  change  in  the  volume  of 
liquids  contained  in  them;  but  that,  on  the  contrary,  we 
fliould  here  fuppofe  the  dilatation  of  glafs  greater  than 
it  is,  and  as  it  would  be  if  it  had  the  fame  expanfibility 
as  the  liquid  ; and  then  diminifh  according  to  that  pro- 
portion 
foumettre  aux  memes  experiences,  en  faifant  Hotter  un  petit  corps  opaque  a leur 
furface,  pour  y pointer,  le  Microfcope.  Cependantje  n’infifte  pas  fur  cette  ap- 
plication cle  la  machine;  parceque  les  expanfions  des  liquidcs  peuvent  etre  ob- 
fervees  dans  des  vafes  dont  on  connoit  la  capacite,  en  y joignant  des  tubes  cy  lin- 
driques;  ce  qui  rend  leur  expanfion  beaucoup  plus  fenfible.  Je  remarquerai  done 
feulement;  qu’i'l  ne  faudroit  pas,  d’apres  la  connoiilance  de  la  dilatabilite  de  la 
matiere  du  tuyau,  reduire  par  le  calcul  fa  capacite,  a ce  qu’elle  feroit  fi  le  verre  ne 
fedilatoit  point,  comme  on  le  fait  a l’egard  des  vafes  pour  connoitre  le  changement 
reel  du  volume  des  liquides  qu’ils  contiennent;  maisqu’au  contraire  il  faudroit  ici 
fuppofer  cette  capacite.  plus  grande,  en  laportant  a ce  qu’elle  feroit,  fi  le  verre 
avoit  la  merae  expanfibilite.  que  le.  liquide;  et  diminuer  dans  cette  proportion 
1’allongement 
