Pyrometry  and  Areometry , &c.  42  ~ 
dilatable  by  heat,  and  laying  them  one  over  the  other,  to 
rivet  them  together  at  one  of  their  ends.  If  then  they 
are  folidly  fufpended  by  the  oppofite  end  of  one  of  the 
rods  only,  and  on  the  free  rod  there  be  marked  a point, 
at  the  level  of  the  point  of  fufpenfion  of  the  other;  thefe 
two  points  will  remain  equally  immoveable,  whatever 
be  the  heat  which  affefts  the  two  rods,  fo  long  as  it 
affedts  them  equally:  for  the  expan  lion  downwards  in 
the  fixed  rod  will  be  compenfated  by  the  expanfion  up- 
wards in  that  which  is  free;  and  confequently,  the 
point  marked  upon  this  will  always  remain  equally  high, 
that  is,  correfponding  in  the  fame  manner  with  the 
point  of  fufpenfion  of  the  other;  fo  the  proportion  of 
expanfions  of  the  two  rods  will  bfe  that  of  equality,  fince 
the  diftances  from  the  point  of  union  of  the  rods  to 
the  two  immoveable  points  will  be  equal ; and  that,  con- 
fequently, 
lie  enfemble  par  un  de  leurs  bouts:  £ on  les  fufpend  folidement  par  le  bout 
oppofe  de  Fune  des  branches  feulement,  -et  qu’on  marque  un  point  fur  la  branche 
libre  vis  a vis  du  point  de  fufpenfion  de  Fautre,  ces  deux  points  refteront 
-egalement  immobiles,  quelle  que  fort  la  chaleur  qui  affe£te  les  deux  branches, 
des  que  ce  (era  egaiement:  car  i’allongement  vers  le  bas  dans  la  branche  fixee, 
fera  compenfc  par  Fallon  gem  ent  vers  le  haut  dans  la  branche  Hbre;  et  par  con- 
fequent  le.  point  marque  fur  celle-ci,  reftera  toujour  s exa£lement  a la  memo 
hauteur,  c’efl  a dire  vis  a vis  du  point  de  fufpenfion  de  Fautre.  Ainfi  ie  rapport 
•des  expanfibilites  des  deux  branches,  fera  celui  d’egalite;  puifque  la  diftance  du 
point  de  reunion  des  branches,  aux  deux  points  immobile?,  fera  la  meme,  et  que 
Vol.  LXVIII.  E e e P*? 
