﻿Chemistry 
  and 
  Physics. 
  59 
  

  

  pheric 
  pressure 
  ; 
  although 
  the 
  percentage 
  difference 
  is 
  not 
  con- 
  

   stant. 
  On 
  adding 
  a 
  little 
  free 
  sulphuric 
  acid 
  to 
  the 
  air 
  solution, 
  

   however, 
  this 
  difference 
  becomes 
  more 
  constant 
  and 
  is 
  higher 
  than 
  

   before. 
  On 
  adding 
  the 
  acid 
  to 
  both 
  voltameters 
  the 
  percentage 
  

   difference 
  becomes 
  constant 
  within 
  the 
  limits 
  of 
  experimental 
  

   error. 
  In 
  this 
  case, 
  where 
  the 
  current 
  density 
  rises 
  above 
  0*01 
  

   ampere 
  per 
  square 
  centimeter 
  of 
  active 
  kathode, 
  there 
  is 
  no 
  prac- 
  

   tical 
  difference 
  between 
  the 
  two 
  deposits. 
  For 
  densities 
  below 
  

   this 
  value 
  however 
  the 
  vacuum 
  deposit 
  is 
  appreciably 
  higher 
  than 
  

   the 
  air 
  deposit. 
  If 
  a 
  curve 
  be 
  drawn 
  to 
  represent 
  the 
  deposits 
  

   obtained 
  in 
  a 
  vacuum 
  at 
  different 
  current 
  densities, 
  it 
  will 
  be 
  ob- 
  

   served 
  to 
  be 
  more 
  regular 
  than 
  the 
  air 
  curve, 
  and 
  to 
  be 
  approxi- 
  

   mately 
  a 
  straight 
  line 
  for 
  densities 
  below 
  O'Ol 
  ampere 
  per 
  square 
  

   centimeter. 
  

  

  In 
  a 
  paper 
  following 
  this, 
  Schuster 
  gives 
  the 
  details 
  of 
  cer- 
  

   tain 
  experiments 
  made 
  by 
  him 
  some 
  years 
  ago, 
  proving 
  that 
  

   when 
  copper 
  is 
  placed 
  in 
  a 
  copper 
  sulphate 
  solution 
  containing 
  

   free 
  sulphuric 
  acid, 
  and 
  the 
  tubes 
  are 
  exhausted 
  of 
  air, 
  the 
  diminu- 
  

   tion 
  in 
  the 
  weight 
  of 
  the 
  copper 
  is 
  quite 
  insignificant 
  compared 
  with 
  

   what 
  takes 
  place 
  in 
  the 
  presence 
  of 
  air. 
  In 
  sulphuric 
  acid 
  alone 
  

   the 
  metal 
  behaves 
  similarly. 
  — 
  Proc. 
  Roy. 
  Soc, 
  lv, 
  66, 
  84, 
  January, 
  

   1894. 
  G. 
  F. 
  B. 
  

  

  7. 
  On 
  the 
  Propagation 
  of 
  Electromagnetic 
  Waves 
  in 
  Ice 
  and 
  

   on 
  the 
  Dielectric 
  Power 
  of 
  this 
  Substance 
  ; 
  '"by 
  M. 
  Blondlot. 
  — 
  In 
  

   a 
  previous 
  note 
  (Comptes 
  Pe?idus, 
  July 
  25, 
  1892) 
  I 
  enunciated 
  

   the 
  following 
  proposition 
  : 
  — 
  The 
  length 
  of 
  the 
  waves 
  which 
  an 
  

   electromagnetic 
  oscillation 
  can 
  emit 
  is 
  the 
  same 
  whatever 
  be 
  the 
  

   insulating 
  medium 
  in 
  which 
  the 
  experiment 
  is 
  made; 
  in 
  other 
  

   words, 
  the 
  wave-length 
  depends 
  on 
  the 
  oscillator 
  alone, 
  just 
  as 
  in 
  

   acoustics 
  the 
  wave-length 
  of 
  a 
  pipe 
  depends 
  only 
  on 
  the 
  length 
  of 
  

   the 
  pipe. 
  

  

  The 
  confirmatory 
  experiments 
  described 
  in 
  the 
  Note 
  cited 
  re- 
  

   ferred 
  to 
  oil 
  of 
  turpentine 
  and 
  to 
  castor 
  oil; 
  the 
  law 
  holds 
  per- 
  

   fectly 
  for 
  both 
  these 
  substances, 
  and 
  everything 
  leads 
  to 
  the 
  

   belief 
  that 
  this 
  will 
  be 
  the 
  same 
  for 
  other 
  dielectrics. 
  

  

  There 
  is, 
  however, 
  a 
  doubt 
  about 
  ice, 
  in* 
  consequence 
  of 
  the 
  

   exceptional 
  properties 
  ascribed 
  to 
  it. 
  The 
  experiments 
  of 
  M. 
  

   Bouty 
  (Comptes 
  Hendus, 
  March 
  7, 
  1892) 
  show 
  in 
  fact 
  that 
  ice 
  has 
  

   a 
  dielectric 
  power 
  of 
  27, 
  that 
  is 
  to 
  say 
  incomparably 
  greater 
  than 
  

   that 
  of 
  all 
  other 
  substances. 
  Suspecting 
  that 
  the 
  law 
  relative 
  to 
  

   the 
  propagation 
  of 
  waves 
  might 
  not 
  apply 
  to 
  a 
  dielectric 
  so 
  differ- 
  

   ent 
  from 
  the 
  others, 
  1 
  resolved 
  to 
  submit 
  the 
  question 
  to 
  experi- 
  

   ment. 
  

  

  For 
  these 
  investigations 
  I 
  availed 
  myself 
  of 
  the 
  intense 
  and 
  

   prolonged 
  frosts 
  of 
  the 
  winter 
  of 
  1892-93. 
  M. 
  M. 
  Dufour 
  has 
  

   helped 
  me 
  in 
  carrying 
  them 
  out, 
  which 
  the 
  rigour 
  of 
  the 
  cold 
  

   rendered 
  difficult 
  and 
  even 
  painful. 
  I 
  thank 
  him 
  for 
  his 
  extreme 
  

   kindness 
  on 
  this 
  occasion. 
  

  

  The 
  method 
  which 
  I 
  adopted 
  was 
  the 
  following, 
  which, 
  with 
  

   slight 
  modifications 
  necessitated 
  by 
  the 
  solid 
  character 
  of 
  the 
  

  

  