﻿472 
  

  

  On 
  the 
  Elecfric 
  Conductivity 
  of 
  Glass. 
  [Jane 
  10, 
  

  

  The 
  polarization 
  which 
  occurs 
  after 
  charging 
  is 
  very 
  marked. 
  Some 
  

   of 
  the 
  later 
  tables 
  of 
  results 
  seem 
  to 
  indicate 
  an 
  increased 
  polarization 
  

   due 
  to 
  increase 
  of 
  temperature. 
  Thus, 
  when 
  at 
  any 
  low 
  temperature 
  the 
  

   conductivity 
  calculated 
  from 
  successive 
  intervals 
  is 
  nearly 
  constant, 
  if 
  

   the 
  temperature 
  is 
  rapidly 
  raised 
  and 
  then 
  kept 
  constant, 
  the 
  conduc- 
  

   tivity 
  at 
  the 
  new 
  temperature 
  diminishes 
  for 
  a 
  short 
  time 
  as 
  if 
  the 
  jar 
  

   had 
  just 
  been 
  charged. 
  

  

  [In 
  such 
  a 
  jar 
  the 
  charge 
  is 
  approximately 
  represented 
  by 
  

  

  I 
  AY 
  

   4tt« 
  ' 
  

  

  where 
  I 
  is 
  the 
  specific 
  inductive 
  capacity 
  of 
  the 
  glass, 
  V 
  the 
  reading 
  of 
  

   the 
  electrometer, 
  and 
  a 
  the 
  thickness 
  of 
  the 
  glass. 
  But 
  if 
  Jc 
  is 
  the 
  spe- 
  

   cific 
  conductivity 
  of 
  the 
  glass, 
  the 
  rate 
  of 
  conduction 
  through 
  it 
  is 
  

  

  JcA-, 
  

   a 
  

  

  and 
  the 
  quantity 
  conducted 
  through, 
  divided 
  by 
  the 
  charge, 
  is 
  equal 
  to 
  

  

  4w7c 
  

   I 
  

  

  Hence 
  

  

  k 
  1 
  difference 
  of 
  Napierian 
  logarithms 
  

  

  I 
  — 
  47r 
  " 
  difference 
  of 
  times 
  

  

  Thus 
  the 
  rapidity 
  of 
  loss 
  given 
  above 
  multiplied 
  by 
  the 
  specific 
  inductive 
  

   capacity, 
  and 
  divided 
  by 
  47r, 
  represents 
  the 
  specific 
  conductivity 
  of 
  the 
  

   glass. 
  

  

  » 
  To 
  determine 
  the 
  following 
  Table 
  of 
  conductivities 
  as 
  measured 
  by 
  

   rapidity 
  of 
  loss, 
  the 
  jar 
  was 
  kept 
  long 
  enough 
  at 
  each 
  temperature 
  for 
  

   the 
  polarization 
  to 
  become 
  insensible. 
  

  

  Temp. 
  F 
  

  

  58° 
  

  

  86° 
  

  

  148° 
  

  

  166° 
  

  

  188° 
  

  

  202° 
  

  

  210° 
  

  

  Rapidity 
  of 
  loss 
  

  

  o-ooo 
  

  

  0-004 
  

  

  0-021 
  

  

  0025 
  

  

  0051 
  

  

  0075 
  

  

  0-084 
  

  

  Rapidity 
  as 
  corrected 
  by 
  a 
  

  

  

  

  

  

  

  

  

  

  000 
  

  

  0004 
  

  

  0018 
  

  

  0-029 
  

  

  0051 
  

  

  0073 
  

  

  0-090 
  

  

  Rapidity 
  as 
  given 
  by 
  the 
  

  

  

  

  

  

  

  

  

  

  0000 
  

  

  0003 
  

  

  0-018 
  

  

  0-029 
  

  

  0051 
  

  

  0-072 
  

  

  0-091 
  

  

  July 
  13.] 
  

  

  The 
  free 
  curve 
  drawn 
  to 
  correct 
  the 
  observed 
  conductivities 
  was 
  found 
  

   to 
  approximate 
  very 
  closely 
  to 
  the 
  logarithmic 
  curve 
  

  

  G=c< 
  

  

  where 
  C 
  is 
  the 
  conductivity 
  at 
  the 
  temperature 
  166 
  + 
  t, 
  c 
  is 
  the 
  con- 
  

   ductivity 
  given 
  by 
  the 
  free 
  curve 
  for 
  166° 
  F., 
  and 
  a 
  is 
  1-027. 
  

  

  Messrs. 
  Bright 
  and 
  Clark 
  found 
  that 
  the 
  conductivity 
  of 
  gutta 
  percha 
  

   followed 
  a 
  similar 
  law. 
  

  

  The 
  author 
  hopes 
  to 
  obtain 
  some 
  definite 
  results 
  with 
  regard 
  to 
  polari- 
  

   zation, 
  and 
  to 
  determine 
  for 
  flint 
  glass 
  the 
  law 
  of 
  temperature 
  and 
  abso- 
  

   lute 
  specific 
  resistance. 
  

  

  