New  experiments  were  made  at  Courbevoie  in  1841,
and  their  results  served  as  bases  for  the  draft  of  a  law
presented  to  the  Chambers  in  1842,  and  especially  for  the
report  of  the  commission  of  the  chamber  of  deputies,  who
had  studied  the  question  conscientiously.
This  is  no  place  to  enter  into  a  detailed  study  of  these
researches,  which  belong  more  properly  to  legislation  and
public  administration  than  to  industrial  mechanics,  and  I
shall  limit  myself  with  a  reference  to  a  publication  made
by  me  in  1842,  under  the  title  of  "  Experiences  sur  le
tirage  des  voitures  et  sur  le&  effets  destructeurs  qu'elles
exercent  sur  les  routes."


KESISTA1STCE  OF  FLUIDS.
299.  The  resistance  of  fluids. — When  a  body  moves
in  a  fluid  mass,  it  necessarily  displaces  the  molecules
of  the  latter,  impressing  upon  them  velocities  in  a
certain  ratio  to  its  own,  and  we  easily  conceive  that  the
inertia  of  the  molecules,  thus  set  in  action,  develops  a
resistance  which  increases  with  the  velocity  of  the  body.
Similar  effects  are  produced  when  a  body  at  rest  or  in
motion  is  shocked  by  a  fluid.
The  manner  in  which  the  fluid  particles  are  divided  at
their  meeting  with  the  body,  depends -much  upon  the
form  and  proportions  of  the  latter,  and  we  see  that  the
resistance  in  question  must  vary  notably  with  these  cir-
cumstances.
This  important  question  of  physical  mechanics  has  for
a  long  time  engaged  the  attention  of  philosophers,  and  we
find  in  the  introduction  to  the  industrial  mechanics  of  M.
Poncelet,  a  complete  analysis  of  all  the  ancient  and
modern  researches  upon  this  matter.  I  only  propose,  in
these  lectures,  to  call  attention  to  the  most  important
cases  in  practice.
