428  Mr.  de  luc  on 
be,  to  be  allured,  that,  whilft  the  fubftanees  compared  are 
warming,  a Microfcope  and  a point  of  fufpenfion  will  be 
Secured  from  being  difturbed  by  any  motion ; which  js 
not  very  difficult. 
Defcription  of  an  injlrument , intended  to  find  out  the  com- 
parative expanfibilities  of  bodies  by  heat. 
I flatter  myfelf,  that  a defcription  will  make  this  in- 
ftrument  fufficiently  underftood  to  render  it  unneceflary 
for  me  to  give  a figure  of  it:  fhould  the  Society,  how- 
ever, be  defirous  of  having  a drawing  of  it,  I fhall  with 
pleafure  obey  their  commands 'w 
The  balls  of  the  inftrument  is  a rectangular  piece  of 
deal-board,  very  ftrait-grained,  two  feet  and  a half  long, 
fifteen  inches  broad,  and  one  inch  and  a half  thick:  it  is 
to  this  that  all  the  other  parts  are  fixed.  The  firft  thing 
I did 
et  un  point  de  fufpenfion  feront  mis  a l’abri  de  tout  mouvement,  tandis  qu’oa 
echauftera  Les  matieres  comparees;  ce  qui  n’efl  pas  bien  difficile. 
Defcription  fun  injlrument  define  a trouver  les  expanfbilites  comparatives  des  corps 
par  la  chaleur . 
Jecrois  pouvoir  me  difpenfer  de  donner  une  figure  de  ma  machine,  pares  que 
j’efpere  qu’une  fimple  defcription  la  fera  comprendre.  Si  cependant  la  Societe 
Royale  fouhaitoit  quejela  fiffe  defliner,  je  me  conformerois  a fon  intention^. 
Une  planche  de  fapin  a fibres  bien  droites,  de  2§  pieds  de  long,  15  pouces  de 
large,  et  i|  pouce  d’epaiffeur,  fait  la  bafe  de  la  machine,.  C’efl  a cette planche 
(c)  See  plate  vii.  fig.  2.  and  its  explanation. 
que 
