&2S  On  Secondary  Rbntgen  Radiation. 
From  calcium  a  radiation  differing  considerably  from  the 
primary  was  produced  exhibiting,  to  a  certain  extent,  the 
polarization  in  the  primary  beam.  From  tin  the  purely 
scattered  radiation  was  entirely  or  almost  entirely  absent. 
Now  it  cannot  be  supposed  that  more  than  an  exceedingly 
small  fraction  of  the  corpuscles  were  displaced  sufficiently  to 
disturb  the  stability  of  the  atom;  hence  the  disappearance  of 
the  scattered  radiation  was  not  due  to  any  instability  during 
the  passage  of  the  primary  pulses. 
The  disappearance  of  scattering  and  the  appearance  of  an 
easily  absorbed  radiation  together  1  oint  to  the  same  cause, 
and  as  all  the  observed  effects  may  be  accounted  for  by  this, 
it  is  improbable  that  an  appreciable  disintegration  sets  in  at 
the  same  atomic  weight. 
Also  if  the  energy  of  secondary  radiation  depenled  on 
there  being  sufficient  electric  intensity  in  the  primary  pulses 
to  produce  disintegration  of  the  atom,  we  should  have  to 
conclude,  as  we  find  intensity  of  secondary  radiation  pro- 
portional to  the  ionization  produced  by  the  primary  in  the 
primary  electroscope  (the  character  remaining  constant),  that 
the  disintegration  produced  in  a  given  metal  by  a  primary 
beam  is  proportional  to  the  ionization  produced  in  a  given 
gas  by  the  same  beam. 
If  we  apply  the  disintegration  theory  to  calcium,  we  must 
conclude  that  the  scattered  radiation  and  the  radiation  due  to 
disintegration  are  in  a  constant  proportion  whatever  be  the 
intensity  of  the  primary,  for  the  absorbability  of  the  mixture 
is  unchanged.     This  appears  very  improbable. 
Again,  the  change  in  character  of  the  secondary  with  that 
of  the  primary  indicates  that  a  considerable  portion  at  least 
of  the  secondary  radiation  is  not  due  to  disintegration,  for  the 
character  of  this  we  should  expect  to  be  independent  of  the 
exciting  cause  and  to  be  characteristic  merely  of  the  atom. 
It  is  significant  also  that  the  secondary  rays  have  been 
invariably  found  to  be  less  penetrating  (yet  not  of  an  entirely 
different  order  of  magnitude)  than  the  primary  producing 
them;  a  result  necessary  to  the  theory  here  given,  and  not  at 
all  likely  on  the  disintegration  theory. 
If  Prof.  Bumstead's  conclusions  on  the  point  are  correct, 
it  appears  probable  that  investigations  on  the  easily  absorbed 
radiation  would  throw  further  light  on  the  subject.  1  hope 
to  make  such  investigations  shortly. 
In  conclusion  I  wish  to  express  my  indebtedness  to  Mr. 
C.  A.  Sadler,  B.Sc,  and  Mr.  A.  L.  Hughes,  for  their  valuable 
assistance  in  conducting  some  of  these  experiments. 
George  Holt  Physics  Laboratory,  LiverpDol. 
