43°  Mr.  de  luc  on 
will  give  it  the  degree  of  friction  one  thinks  proper.  I 
preferred  this  mode  to  that  of  moving  the  Microfcope 
by  a fcrew,  becaufe  this  laft  would  have  required  metal, 
which  is  more  fufceptible  of  the  impreffions  of  heat  than 
deal  is ; and  becaufe  the  execution  of  it  would  have  been 
longer,  and  more  expenfive,  from  the  degree  of  perfec- 
tion it  would  have  required,  whilft  this  fimple  method 
has  fucceeded  perfectly  well. 
The  inner  Hiding  frame,  which  is  likewife  of  deal,  keeps 
the  tube  of  the  Microfcope  in  an  horizontal  pofition, 
and  in  great  part  without  the  frame,  infomuch  that  the 
end  which  carries  the  lens  is  but  little  within  the  fpace 
between  the  frame  and  the  board.  This  Microfcope 
is  conftrudted  in  fuch  a manner  as  that  the  object 
obferved  may  be  an  inch  diftant  from  the  lens,  and 
it 
quatre  vis  Iui  cbnne  le  degre  de  frottement  que  Ton  veut.  J’ai  prefere  ce 
moyen,  a celui  de  conduire  le  Microfcope  par  une  vis;  parce  que  ce  dernier 
auroit  exige  du  metal,  plus  fufceptible  des  impreffions  de  la  chaleur  que  le  fapin; 
et  que  1’execution  auroit  ete  plus  longue  et  plus  difpendieufe,  par  la  perfc£lion 
qu’elle  eut  exige : tandis  que  cette  voye  fimple  a parfaitement  reuffi. 
Le  chaffis,  qui  eft  auffi  de  fapin,  tient  le  tube  du  Microfcope  fitue  horizon- 
talement,  et  en  grande  partie  au  dehors  du  cadre;  tellement  que  le  bout  qui  porte 
la  lentille  n’eft  que  fort  peu  en  ded.ns  de  Pefpace  compris  entre  le  cadre  et  la 
planche.  Ce  Microfcope  eft  conftruit  de  maniere,  que  Pobjet  obferve  peut  etre 
4 a ub 
