Mr.  DE  LUC  OH 
444 
in  through  a long  tunnel,  by  which  means  every  thing 
remained  quiet  during  the  time  of  the  experiment. 
By  comparing  thefe  two  obfervations  together,  it 
fhould  feem,  that  when  the  igneous  fluid  is  agitated  for 
fome  time,  in  fubftances,  the  particles  of  which  have  not 
that  ftrong  tendency  towards  each  other  which  confti- 
tutes  elafticity,  it  produces  fome  change  in  the  arrange- 
ment of  thefe  particles,  which  hinders  the  compound 
from  refuming  the  fame  bulk  upon  the  return  of  the 
fame  degree  of  heat;  a change  which  there  is  not  time  to 
bring  about,  when  the  variations  are  fudden,  if  there  be 
at  leaft  fome  elafticity  in  the  matter. 
In  fupport  of  this  we  already  know,  that  glafs,  the 
moft  elaftic  of  known  fubftances,  is  not  fubjedt  to  this 
irregularity,  as  I ftiall  foon  fliew ; that  brafs,  which  is 
much  lefs  elaftic,  is  fenfibly  affedted  by  it;  and  that  lead, 
the 
d’un  entonnoir  a long  tuyau.  Ainfi  tout  reftoit  tranquille  pendant  Pexperience- 
Ces  deux  obfervations  comparees  femblent  done  indiquer,  que  lorfque  le 
Buide  igne  s’agite  pendant  quelque  terns  dans  les  matieres  dont  les  particules 
n’ont  pas  entr’elles  cette  forte  tendance  qui  fait  l’elafticite,  il  produit  dans  Par- 
rangement  de  ces  particules  quelque  ebangement,  qui  empeebe  les  eompofes  de 
reprendre  exa£Vement  le  meme  volume  quand  le  meme  degre  de  chaleur  revient  r 
ebangement  qui  n’a  pas  le  terns  de  s’effe&uer,  lorfque  les  variations  font  fubites^ 
**il  y a du  moins  quelque  elafticite  dans  lamatiere. 
Nous  avons  deja  pour  fondement  de  eette  idee,  que  le  verre,  la  plus  elaftique 
de s matieres  connues,  n’eft  pas  fujet  a cette  irregularite,  comme  je  le  montrerai 
bientot;  que  le  leton*  biea  moins  elaftique,  Pa  fenfiblement  y et  que  le  plumb, 
lc 
