On  the  Constitution  of  Natural  Radiation.  123 
if  four  equally  spaced  electrons  revolve  in  a  ring,  the  radiation 
is  feeble  and  its  frequency  is  four  times  that  of  revolution. 
If  the  disposition  of  equal  spacing  be  disturbed,  there  must 
be  a  tendency  to  recovery  and  to  oscillations  about  this  dis- 
position. These  oscillations  may  be  extremely  slow  ;  but 
nevertheless  frequencies  will  enter  into  the  radiation  once, 
t^vice,  and  thrice  as  great  as  that  of  revolution,  and  with 
intensities  which  may  be  much  greater  than  the  original 
radiation  of  fourfold  frequency. 
An  apparently  formidable  difficulty,  emphasised  by  Jeans, 
stands  in  the  way  of  all  theories  of  this  character.  How 
can  the  atom  have  the  definiteness  which  the  spectroscope 
demands  ?  It  would  seem  that  variations  must  exist  in  (say) 
hydrogen  atoms  which  would  be  fatal  to  the  sharpness  of  the 
observed  radiation  ;  and  indeed  the  gradual  change  of  an 
atom  is  directly  contemplated  in  view  of  the  phenomena  of 
radioactivity.  It  seems  an  absolute  necessity  that  the  large 
majority  of  hydrogen  atoms  should  be  alike  in  a  very  high 
degree.  Either  the  number  undergoing  change  must  be 
very  small  or  else  the  changes  must  be  sudden,  so  that  at  any 
time  only  a  few  deviate  from  one  or  more  definite  conditions. 
It  is  possible,  however,  that  the  conditions  of  stability  or 
of  exemption  from  radiation  may  after  all  really  demand  this 
deflniteness,  notwithstanding  that  in  the  comparatively  simple 
cases  treated  by  Thomson  the  angular  velocity  is  open  to 
variation.  According  to  this  view  the  frequencies  observed 
in  the  spectrum  may  not  be  frequencies  of  disturbance  or  of 
oscillations  in  the  ordinary  sense  at  all.  but  rather  form  an 
essential  part  of  the  original  constitution  of  the  atom  as 
determined  by  conditions  of  stability. 
Terling  Place,  Witham,  Nov.  8. 
VIII.    On  the  Constitution  of  Natural  Radiation. 
By  Lord  Rayleigh,  'O.M.,  F.B.S* 
THE  expression  of  Prof.  Earmolds  views  in  his  paper  j 
"  On  the  Constitution  of  Natural  Radiation  "  is  very 
welcome.  Although  it  may  be  true  that  there  has  been  no 
direct  contradiction  public  and  private  communications  have 
given  me  an  uneasy  feeling  that  our  views  are  not  wholly 
in  harmony;  nor  is  this  impression  even  now  removed.  It 
may  conduce  to  a  better  understanding  of  some  of  these  im- 
portant  and    difficult    questions    if    without    dogmatism    1 
*  Communicated  by  the  Author, 
f  Phil.  Mag.  vol.  x,  p.  574  (190o). 
