76.  Eytelweirfs  apparatus. — This  learned  engineer
seems  to  have  been  the  first  to  entertain  the  idea  of  com-
bining a  known  uniform  motion  with  that  to  be  deter-
mined, so  as  to  obtain  a  trace  of  simultaneous  motions,
from  which  might  be  deduced  the  condition  of  the  un-
known motion.
For  his  experiments  upon  the  hydraulic  ram,  he  used
an  endless  band  of  paper,  (Figs.  31  and  32,)  rolled  upon
two  cylinders,  to  which  a  regular  motion  was  imparted


OBSERVATION   OF    THE   LAWS   OF   MOTION.
by  the  hand.     The  lengths  of  the  paper  passed  were  then
nearly  proportional  to  the  time.     A  style  fixed  to  the


J_L


II     ,

r^


=L  L


Fig.  31.
stem  of  the  valves  traced  upon  this  band  a  curve  whose
ordinates  were  the  spaces  described.
M.  Eytelwein  could,  by  means  of  this  imperfect  con-
trivance, nearly  determine  the  intervals  of  time  between
the  opening  and  shutting  of  the  valves.
But  we  know  that  the  motion  imparted  by  the  hand
could  not  have  been  uniform,  and  that  this  disposition
could  not  give  very  exact  results.
77.  New  apparatus. — For  experiments  made  at  Metz,
upon  friction,  and  for  other  researches,  at  M.  Poncelet's
suggestion,  I  made  use  of  a  combination  of  a  known  mo-
tion with  one  whose  law  was  to  be  determined.
I  have  since  modified  the  arrangement  of  this  machine,
and  that  deposited  in  the  repository  of  arts  and  machines
was  made  in  the  following  manner,  (Figs.  33  and  34 :)
a  plate  1.05ft-  in  diameter,  perfectly  plane,  receives  a
uniform  motion  by  means  of  a  weight  hung  to  a  first  axle.
