Mr.  de  luc  on 
422 
phyflcal  effects  render  them  indeed  more  apparent,  hut 
do  not  at  all  contribute  to  their  exadt  menfuration. 
I had  heard  the  ingenious  Mr.  ramsden  fay,  that 
he  had  a notion  of  a Pyrometer  different  from  all  that 
had  been  invented;  and  knowing  his  great  fkill  in 
philofophical  and  mechanical  matters,  I applied  to  him, 
and  prefled  him  to  execute  his  idea.  The  multitude 
of  his  other  engagements  prevented  his  complying 
with  my  requeft;  and  he  advifed  me  to  look  no  far- 
ther for  the  proportions  of  the  expanlions  of  brafs  and 
glafs  than  to  Mr.  sme atom's  experiments,  which  he 
looked  upon,  with  reafon,  as  the  beft  that  had  been 
madefjf.  Still,  however,  upon  my  deliring  him  to  ex- 
plain by  what  means  he  thought  of  being  able  to  cor- 
rect the  faults  of  the  ancient  inftruments,  he  was  kind 
(a)  Phil.  Tranf.  1754. 
enough 
ainfi  les  petits  efFets  phyfiques,  c’efl  bien  les  rendre  plus  apparents,  mais  nulle- 
ment  les  melurer  avec  exactitude. 
J’avois  ou'i  dire  a l’ingenieux  Mr.  ramsden,  qu’il  avoit  l’idee  d’un  Pyrometre 
different  de  tous  les  autres;  et  connoifFant  fa  grande  intelligence  dans  les  matieres 
de  phyfique  et  de  mechanique,  j’eus  recours  a lui,  et  je  le  prefFai  d’executer  fon 
plan.  Mais  la  multitude  des  objets  qui  l’occupent  l’en  empecha,  et  il  me  con- 
feilla  de  m’en  tenir  pour  le  rapport  des  expanfions  du  leton  et  du  verre,  aux 
experiences  de  Mr.  smeaton,  qu’il  regardoit  avec  raifon  commeles  plusfures*. 
Je  priai  cependant  Mr.  ramsden  de  m’expliquer  par  quel  moyen  il  comptoit 
de  pouvoir  eviter  les  defauts  des  machines  anciennes;  et  il  eut  la  complaifance 
# Phil.  Tranf.  1 7 54. 
de 
