608        The  Dielectric  Strain  along  the  Lines  of  Force. 
in  opposition  to  the  results  of  Cantons,  who  found  the 
expansion  greater  than  the  theoretical  value.  They  do  not 
disagree  with  those  of  Mr.  More,  supposing  he  has  used 
Thuringian  or  a  similar  kind  of  glass. 
In  the  above-mentioned  paper  Mr.  More  savs : — 
(1)  That  our  method  was  "  faulty." 
(2)  That  "  we  had  attempted  to  show  that  the  real  elasticity 
of  glass  was  greater  when  obtained  from  electrical  stress  than 
when  found  by  mechanical  and  acoustical  methods." 
(3)  That  we  had  mistaken  the  nature  of  the  problem  in 
regarding  the  effect  as  being  due  to  a  variation  of  elasticity 
of  electrified  and  not-electrified  glass,  while  the  effect  obtained 
by  us  was  produced  partly  by  the  faults  of  the  method 
employed,  partly  by  the  alteration  of  the  inductive  capacity 
of  glass  by  pressure. 
As  to  (1)  :  We  have  improved  the  method  of  Quincke 
until  the  observations  showed  sufficient  regularity  for  the  same 
kind  of  glass.  It  seems  that  Mr.  More  distrusts  the  exactness 
of  our  method  especially  for  the  reason  that  the  results 
obtained  were  very  different  with  different  kinds  of  glass. 
■J  ~z> 
We  will  show  afterwards  that,  on  the  contrary,  these  differ- 
ences are  an  indirect  proof  of  the  correctness  of  onr  statements. 
As  to  (2)  :  Mr.  More  misunderstood  what  we  called  "the 
coefficient  of  elasticity  by  electrostriction."  We  introduced 
this  coefficient  because  it  enabled  us  to  compare  in  a  simple 
way  our  results  for  different  forms  of  tubes  and  spheres.  He 
has  overlooked  that  we  have  made  some  experiments  (p.  1258) 
expressly  for  the  purpose  of  proving  that  there  is  no  real 
change  of  the  coefficient  of  elasticity  by  electrification. 
As  to  (3)  :  Mr.  More  has  overlooked  also  that  we  published 
some  month sjater  a  second  part  of  our  investigation,  entitled 
"  Ueber  die  Anderung  der  Dielectricitats-constante  des  Glases 
mit  dem  Druck "  *.  In  this  paper  we  tried  to  examine 
if  there  was  an  alteration  of  the  inductive  capacity  with 
mechanical  pressure  in  the  same  glass  tubes  as  we  had  used 
in  the  experiments  on  electrostriction.  The  result  was,  that 
he  same  kinds  of  glass,  in  which  the  expansion  by  elec- 
trification was  found  too  small,  showed  an  increase  of  the 
inductive  capacity  with  pressure.  The  agreement  was  not 
only  in  sign,  but  even  in  value. 
We  are  glad  to  see  that  in  the  principal  points  Mr.  More 
agrees  totally  with  our  views,  viz.,  that  there  exist  no  other  real 
forces  in  electrostriction  than  the  pressure  of  the  armatures. 
But  we  think  we  have  done  a  little  more  than  he.  Mr.  More 
has  shown  that  in  some  cases  there  was  no  electrostriction, 
and   suggested,  without   ascertaining  it  by  experiments,  that 
*  Ann.  d.  Physik  (4)  xi.  p.  619  (1903). 
