Am.  jour.  Pharm. }    Viezus  on  Constitution  of  the  Atom.  191 
April,  191o.       /  ,  ■ 
nomena  occur  is  unknown,  whether  we  consider  electrons  projected 
by  ultraviolet  light,  Rontgen  rays,  or  gamma  rays. 
Planck's  Constant. — When  in  a  reflecting  enclosure  there  is  a 
heated  body  and,  necessarily,  ether,  the  former  has  a  limited  number 
of  degrees  of  freedom,  and  the  latter  an  unlimited  number.  It  may, 
therefore,  be  expected  that,  as  theory  appears  to  indicate,  the  energy 
of  the  body  would  decrease  and  that  of  the  ether  increase,  particu- 
larly towards  vibrations  of  the  shorter  wave-lengths.  Experiment 
proves  that  this  does  not  occur,  and  that  the  distribution  of  energy 
is  utterly  different  from  that  which  Newtonian  mechanics  demand. 
Planck  found  himself  able  to  explain  this  distribution  only  on  the 
supposition  that  energy  could  leave  the  oscillators  in  the  body  by 
exact  quanta,  the  magnitude  of  which  was  in  each  case  proportional 
to  the  frequency  of  the  oscillator,  or  equal  to  hn.  Shortly  before  his 
death  Poincare  thoroughly  investigated  this  hypothesis  and  con- 
cluded that  an  explanation  on  the  basis  of  Planck's  hypothesis  was 
inevitable,  and  that  no  other  view  was  in  accordance  with  observed 
radiation  phenomena.  An  able  summary  of  the  whole  subject  has 
been  given  by  Jeans  in  a  report  published  by  the  Physical  Society 
of  London.5  We  have,  therefore,  a  unique  situation  in  physics.  The 
quantity  h  has  been  introduced  and  its  magnitude  determined  without 
our  having  any  approximate  idea  of  what  h  represents.  To  the 
student  of  radio-activity  it  is  the  ratio  of  the  number  of  units  of  the 
kinetic  energy  of  the  projected  electron,  divided  by  the  frequency 
of  the  incident,  electromagnetic  disturbance,  or  possibly  by  some 
exact  multiple  of  that  frequency. 
Rontgen  Rays  and  Crystal  Re-flection. — It  was  foreseen  by  Laue, 
at  a  time  when  the  potentialities  of  Rontgen  rays  appeared  almost 
exhausted,  that  these  rays  would  be  scattered  in  a  definite  direction 
from  any  set  of  orderly  parallel  planes  in  which  the  atoms  of  a 
crystal  are  arranged.  An  analogy  may  be  useful.  If  troops  with 
fixed  bayonets  are  not  drawn  up  in  rank  the  sunlight  reflected  from 
the  bayonets  will  give  to  a  spectator  a  glint  here  and  there.  In  well- 
dressed  ranks,  however,  a  spectator  will  in  some  positions  see  no 
reflections,  but  in  other  positions,  when  the  angles  of  reflection  and 
incidence  are  equal,  he  will  obtain  a  powerful  flash  from  all  the 
bayonets  in  all  the  ranks. 
5  "  Report  on  Radiation  and  the  Quantum  Theory,"  by  J.  H.  Jeans,  The 
Electrician  Printing  Company,  Fleet  Street,  London. 
