Secondary  Rontgen  Radiation.  815 
calcium  and  lime  were  among  the  transforming  substances. 
Aluminium  also  belonged  to  the  former  class,  while  calcium, 
a  substance  of  less  density,  belonged  to  the  latter. 
On  the  other  hand,  all  the  elements  in  the  former  class  had 
atomic  weights  lower  than  any  in  the  latter  class,  and  the 
radiation  proceeding  from  a  compound  was  such  as  would  be 
obtained  by  a  mixture  of  the  radiations  proceeding  from  the 
constituent  elements. 
These  experiments  indicated  that  the  character  of  secondary 
radiation  set  up  by  a  given  primary  depends  upon  the  atoms 
subject  to  that  radiation,  and  not  to  any  great  extent,  if  at  all, 
on  their  distances  apart  or  on  their  combination  with  atoms 
of  other  substances. 
Absence  of  Purely  Scattered  Radiation. 
Tn  further  investigating  the  secondary  rays  from  substances 
of  higher  atomic  weight,  experiments  were  made  to  ascertain 
if  the  radiation  consisted  of  a  radiation  such  as  was  found  to 
proceed  from  substances  of  lower  atomic  weight  superposed 
on  a  more  easily  absorbed  radiation. 
The  radiation  from  tin  when  placed  in  the  primary  beam 
was  studied  by  the  method  described  in  a  previous  paper. 
The  absorbability  of  the  radiation  was  measured  by  placing 
successive  layers  of  thin  aluminium  in  front  of  the  electro- 
scope through  which  the  secondary  beam  passed.  The 
ionization  was  initially  large  ;  but  as  sheet  after  sheet  of 
aluminium  was  placed  in  the  path  of  the  secondary  radiation, 
the  reduction  was  so  great  that  the  resultant  ionization  pro- 
duced in  the  secondary  electroscope  was  found  to  be  much 
less  than  what  would  have  resulted  if  simple  scattering  had 
occurred  in  the  tin  such  as  was  found  in  substances  of  low 
atomic  weight.  That  is,  taking  account  of  the  absorption  of 
the  primary  beam  in  the  plate  of  tin  and  of  the  secondary  in 
the  same  plate  and  in  the  aluminium  absorbing  plates,  if  the 
same  percentage  had  been  scattered  as  was  found  from  light 
atoms,  a  much  greater  ionization  would  have  been  produced 
than  was  actually  measured.  The  absorptions  of  primary 
and  secondary  rays  were  determined  by  separate  experiment. 
Thus  the  secondary  radiation  was  found  to  consist  almost 
entirely,  if  not  entirely,  of  a  completely  transformed  radiation. 
Temperature,  Electric  Conductivity,  Magnetic  Permeability. 
To  determine  if  the  character  of  secondary  radiation  was  in 
any  way  connected  with  the  temperature,  electric  conduc- 
tivity,  or   magnetic  property  of  the  radiator,  a  grating  was 
