Decay  of  Torsional  Stress  in  Solutions  of  Gelatine.     £4:1 
unci  platinum  give  solutions  in  water  and  ethyl  malonate  in 
which  the  particles  are  negatively  charged. 
3.  The  electro-positive,  oxidizable  metals  give  solutions  in 
water,  methyl  alcohol,  and  ethyl  alcohol  in  which  the  particles 
are  always  positively  charged. 
4.  The  velocities  of  the  particles  under  a  known  electric 
force  have  been  determined  and  the  potential  differences 
between  the  liquid  and  the  particle  have  been  deduced  by 
using  the  formula  . 
&  V  —  !LV 
"K  '  X  ' 
My  best  thanks  are  due  to  Professor  J.  J.  Thomson  for  his 
kindly  interest  and  advice  during  the  course  of  the  experi- 
ment. I  also  wish  to  acknowledge  heartily  the  many  helpful 
suggestions  which  Mr.  W.  B.  Hardy  has  kindly  given  me. 
Cavendish.  Laboratorv, 
Sept.  1905. 
XXXIX.  On  the  Decay  of  Torsional  Stress  in  Solutions  of 
Gelatine.  By  A.  0.  Rankine,  D.Sc,  Assistant  in  the 
Physics  Department,  University  College,  London  *. 
THE  results  of  the  experiments  on  the  time  rate  of  change 
of  stress  in  lead  wires  under  constant  strain,  published 
in  the  Phil.  Mao-.  Oct.  1904,  suggested  an  investigation  of 
the  laws  governing  this  variation  in  passing  from  purely 
viscous  to  perfectly  elastic  bodies.  Lead  exhibits  both  elastic 
and  viscous  properties  to  a  marked  extent,  but  does  not  obey 
the  mathematically  deduced  laws  of  Maxwell  for  such  bodies. 
The  experimental  curve  of  stress  against,  time  when  the 
stress  remains  constant  is  not  of  the  form  W  =  W0e-A*,  but 
is  represented  fairly  accurately  by  the  equation 
W  =  W0-alog(^  +  l). 
The  question  arises,  ';  Does  a  similar  law  hold  when  the 
viscous  and  elastic  properties  are  combined  in  proportions 
differing  from  those  in  lead  ;  and,  if  not,  how  does  the  law 
change  in  passing  from  the  perfectly  elastic  to  the  purely 
viscous  cases  ?  "  In  order  to  rind  an  answer  experimentally, 
•one  must  be  provided  with  a  series  of  substances  of  the  same 
kind  possessing  elastic  and  viscous  properties  combined  in 
different  proportions  and  extending  from  the  purely  viscous 
on  the  one  side  to  the  perfectly  elastic  on  the  other.  Now 
solutions  of  gelatine  in  water  fulfil  these  conditions.  Solu- 
tions of  very  low  concentration  possess  no  elastic  properties, 
Communicated  by  Prof.  F,  T.  Trouton,  F.R.S 
