Surface  Elasticity  of  Saponine  Solutions.  317 
It  is  in  no  perfunctory  spirit  that  I  wish  to  express  my 
thanks  to  Professor  J.  J.  Thomson  for  permission  to  work 
in  the  Cavendish  Laboratory  and  for  the  help  which  I  con- 
stantly derived  from  his  advice  and  suggestions,  some  of 
which  were  vital  to  the  success  of  the  experiments.  I  take 
pleasure  in  acknowledging  my  great  indebtedness  to  him. 
Conclusions. 
The  present  experiments  indicate  that  when  Bontgen  rays 
are  equally  absorbed  in  lead  and  in  zinc,  approximately  twice 
as  much  heat  is  generated  in  the  lead  as  in  the  zinc.  It 
does  not  appear  possible  to  attribute  this  result  to  errors  in 
the  measurements  or  in  the  theory  underlying  the  experi- 
mental method. 
To  account  for  this  effect  the  writer  has  been  able  to  think 
of  only  one  hypothesis  which  is  not  in  more  or  less  direct 
conflict  with  experimental  facts.  This  hypothesis  is  that,  by 
means  of  Rontgen  rays,  the  atoms  of  certain  elements  may  be 
artificially  broken  up  and  that  the  energy  thus  liberated 
forms  a  part  (and  perhaps  the  greater  part)  of  the  energy 
which  appears  when  the  rays  are  absorbed  by  matter. 
New  Haven,  Corni.,  U.S.A. 
Oct.  20,  1905. 
XXV.  On  the  Surface  Elasticity  of  Saponine  Solutions.  By 
S.  A.  Shorter,  L>.Sc,  Assistant  Demonstrator  in  the 
Physical  Laboratory  of  the  University  of  Leeds  *. 
f  I^HE  question  of  the  concentration  of  dissolved  substances 
JL  in  the  surface-layers  of  solutions  has  been  the  subject 
of  much  research  since  the  time  of  Plateau's  well-known 
experiments  on  the  superficial  viscosity  of  liquids.  The 
present  paper  deals  with  the  specially  interesting  example  of 
this  phenomenon  afforded  by  solutions  of  saponine.  The 
investigation  may  be  divided  into  three  parts : — 
(1)  Examination  of  the  mechanical   properties   of    the 
surface-layer  by  means  of  the  torsion- balance  ; 
(2)  Theoretical  investigation  of  the  effect  of  a  viscous- 
elastic  medium  on  the  motion  of  the  disk  of  the 
torsion-balance  ; 
(3)  Absolute  measurement  of  the  surface-rigidity. 
*  Communicated  by  the  Author. 
