﻿1875.] 
  

  

  Electric 
  Conductivity 
  of 
  Glass. 
  

  

  469 
  

  

  hollow 
  glass 
  globe 
  with 
  a 
  long 
  stem. 
  C 
  is 
  a 
  brass 
  insulator 
  with 
  pumice 
  

   and 
  sulphuric 
  acid, 
  to 
  keep 
  the 
  stem 
  free 
  from 
  moisture. 
  C 
  is 
  supported 
  

   on 
  a 
  stand 
  resting 
  on 
  the 
  table. 
  A 
  wooden 
  clamp 
  supports 
  A 
  B 
  at 
  A. 
  

   B 
  D 
  is 
  covered 
  with 
  tinfoil 
  or 
  with 
  wet 
  linen 
  cloth. 
  W 
  is 
  water 
  inside 
  

   the 
  globe. 
  

  

  Eig. 
  1. 
  Kg. 
  2. 
  

  

  For 
  a 
  lecture 
  illustration 
  Mr. 
  M'Earlane, 
  on 
  March 
  13th, 
  1874, 
  charged 
  

   a 
  flint-glass 
  jar, 
  the 
  globe 
  of 
  which 
  was 
  13 
  centims. 
  in 
  diameter 
  and 
  

   about 
  0*13 
  centim. 
  thick. 
  The 
  inside 
  coating 
  was 
  put 
  to 
  earth 
  by 
  

   means 
  of 
  a 
  wire 
  ; 
  the 
  outside 
  was 
  connected 
  with 
  the 
  electrometer 
  and 
  

   then 
  charged. 
  The 
  wire 
  was 
  then 
  withdrawn 
  from 
  the 
  inside, 
  and 
  the 
  

   stem 
  was 
  sealed 
  at 
  E. 
  On 
  March 
  20th 
  B 
  D 
  was 
  again 
  insulated 
  and 
  

   connected 
  with 
  the 
  electrometer 
  ; 
  the 
  stem 
  was 
  broken 
  at 
  E, 
  and 
  the 
  

   inside 
  put 
  to 
  earth 
  as 
  before. 
  The 
  original 
  charge 
  was 
  2170. 
  At 
  the 
  

   end 
  of 
  a 
  week 
  the 
  charge 
  was 
  found 
  to 
  be 
  1952. 
  The 
  week's 
  loss 
  was 
  

   218, 
  or 
  10 
  per 
  cent. 
  

  

  The 
  jar 
  was 
  again 
  sealed 
  on 
  March 
  20th 
  with 
  a 
  charge 
  of 
  1875. 
  On 
  

   April 
  7th 
  the 
  charge 
  w 
  r 
  as 
  1332 
  ; 
  so 
  that 
  the 
  loss 
  in 
  18 
  days 
  w 
  r 
  as 
  

   543, 
  or 
  28 
  per 
  cent, 
  of 
  the 
  whole 
  charge. 
  

  

  On 
  Jan. 
  5th, 
  1875, 
  the 
  author 
  gave 
  a 
  charge 
  of 
  1465 
  to 
  a 
  flint-glass 
  jar. 
  

   On 
  March 
  16th 
  the 
  electricity 
  had 
  all 
  disappeared. 
  Another 
  flint-glass 
  

   jar 
  charged 
  to 
  1048 
  on 
  Jan. 
  5th, 
  when 
  opened 
  on 
  March 
  16th 
  had 
  a 
  

   charge 
  of 
  144, 
  the 
  loss 
  in 
  70 
  days 
  being 
  904, 
  or 
  86 
  per 
  cent. 
  

  

  