To  sum  up  :  cathode  rays  consist  of  streams  of
electrons  or  particles  of  negative  electricity  ;  each
electron  is  a  charge  of  4-78 xio~10  electrostatic
unit ;  each  atom  of  hydrogen  deprived  of  an
electron  forms  an  ion  ;  it  is  "  positively  charged/'
and  the  charge  which  the  atom  loses  on  becoming
an  ion  has  the  same  value,  viz.  478 xio"10
126


ELECTRONS

electrostatic  unit.  And  as  the  mass  of  an  electron
is  known  to  be  i/i83oth  of  that  of  an  atom  of
hydrogen,  and  as  the  mass  of  an  atom  of  hydrogen
(see  Perrin,  p. -no)  is  1-63  X  ioo~24  gram,  that  of  the
electron  is  o*8xio~27  gram.  It  is  the  smallest
mass  of  which  we  know  the  existence,  but  its
combination  with  or  loss  by  atoms  of  other
elements  profoundly  modifies  their  properties.
127


CHAPTER    IX
ELECTRONS   AND    MATTER

IF  the  reader  will  refer  to  p.  51,  he  will  re-
collect that  electrons  can  attach  themselves  to
matter ;  in  fact,  they  behave  more  or  less  as  if  they
were  chemical  elements,  forming  compounds  with
the  recognized  elements,  just  as  elements  combine
among  themselves.  Indeed,  they  appear  to  be
essential  constituents  of  all  compounds,  and
probably  of  most,  if  not  all,  so-called  elements.
For  the  elements  themselves  would  appear  to
be  only  unusually  stable  compounds.  The
condition  of  their  stability  is  their  retaining  their
combined  electrons  ;  to  separate  them  from  the
constituent  electrons  requires  the  absorption  of
much  energy,  as  a  rule  ;  and  when  separated,  the
change  results  in  what  must  be  termed  different
forms  of  matter.
