2         MOLECULAR  DISSYMMETRY  OP  ORGANIC  PRODUCTS. 
The  Chemical  Society  has  been  gratified  by  the  eagerness  with  which 
many  young  men  of  learning  have  taken  seats  among  the  audience.  It 
has  especially  marked  the  sympathetic  encouragement  given  to  its  labors 
by  the  presence  of  Messrs.  Balard,  Claude  Bernard,  Delafosse,  Fremy, 
Serret,  members  of  the  Academy  of  Sciences. 
May  I  be  permitted,  moreover,  to  especially  thank,  in  my  name  and  in 
the  name  of  the  Society,  our  illustrious  President,  M.  Dumas,  whose  lofty 
and  benevolent  patronage  has  always  served  science  almost  as  much  as 
his  immortal  works.  L.  Pasteur. 
Paris,  1860. 
FIRST  LECTURE. 
At  the  close  of  the  year  1808,  Malus  announced  that  light 
reflected  from  all  bodies,  whether  opaque  or  diaphanous,  ac- 
quired very  extraordinary  new  properties,  which  essentially 
distinguished  it  from  light  transmitted  directly  from  luminous 
bodies. 
The  modification  which  light  undergoes  in  the  act  of  reflection 
Malus  denominated  'polarization.  Later,  this  was  designated 
under  the  name  of  plane  of  polarization  of  the  ray,  the  plane  of 
reflexion  itself,  that  is  to  say,  the  plane  passing  by  the  incident 
ray  and  the  normal  to  the  reflecting  surface. 
Malus  did  not  limit  his  discoveries  on  polarized  light  to  this. 
It  had  long  been  known  that  a  ray  of  direct  light  always  sepa- 
rated into  two  white  fasciculi,  of  the  same  intensity,  in  its 
passage  through  a  rhomboid  of  carbonate  of  lime.  The  flame 
of  a  candle,  observed  by  the  aid  of  such  rhomboid,  is  always 
double,  and  the  two  images  have  the  same  brightness. 
Huygens  and  Newton  had  observed  that  light,  which  has 
passed  through  a  crystal  of  Iceland  spar,  no  longer  comports 
itself  like  direct  light.  So,  looking  through  a  new  rhomboid  at 
one  or  the  other  of  the  two  images  of  the  candle  we  have  just 
mentioned  :  1.  There  will  not  always  be  bifurcation  cf  the  ray: 
2.  When  there  is  bifurcation,  the  two  new  images  will  not  have 
the  same  intensity.  Light,  which  has  traversed  a  bi-refrangent 
crystal,  is  different,  then,  from  natural  or  direct  light.  This 
admitted,  Malus  proved  that  the  modification  impressed  upon 
light  by  double  refraction  was  identical  with  that  which  re- 
flexion produces  from  the  surface  of  opaque  or  diaphanous 
