﻿470 
  Scientific 
  Intelligence. 
  

  

  to 
  blue. 
  The 
  theory 
  of 
  the 
  method 
  is 
  still 
  unsettled. 
  — 
  Nature, 
  

   March 
  21, 
  1895. 
  j. 
  t. 
  

  

  8. 
  Silvering 
  Glass. 
  — 
  To 
  a 
  physicist 
  any 
  method 
  of 
  silvering 
  

   glass 
  which 
  will 
  replace 
  the 
  method 
  with 
  Rochelle 
  salts 
  or 
  the 
  

   Martin 
  process 
  is 
  of 
  especial 
  interest. 
  M. 
  M. 
  Auguste 
  and 
  Louis 
  

   Lumiere 
  describe 
  the 
  following 
  method 
  : 
  To 
  100 
  cubic 
  centi- 
  

   meters 
  of 
  a 
  10 
  per 
  cent 
  solution 
  of 
  silver 
  nitrate 
  ammonia 
  is 
  

   added 
  drop 
  by 
  drop 
  until 
  the 
  precipitate 
  formed 
  is 
  redissolved. 
  

   Too 
  much 
  ammonia 
  must 
  not 
  be 
  added 
  at 
  first, 
  for 
  this 
  might 
  pre- 
  

   vent 
  the 
  formation 
  of 
  the 
  precipitate. 
  The 
  volume 
  of 
  the 
  solu- 
  

   tion 
  is 
  increased 
  to 
  a 
  liter 
  by 
  the 
  addition 
  of 
  distilled 
  water. 
  

   This 
  is 
  solution 
  A. 
  Solution 
  Bis 
  made 
  by 
  diluting 
  commercial 
  

   Formaldehyde 
  of 
  40 
  per 
  cent 
  with 
  distilled 
  water 
  so 
  as 
  to 
  form 
  

   a 
  1 
  per 
  cent 
  solution. 
  Solution 
  B 
  can 
  be 
  kept 
  for 
  some 
  time. 
  

   Two 
  volumes 
  of 
  A 
  are 
  rapidly 
  mixed 
  with 
  one 
  volume 
  of 
  B 
  and 
  

   the 
  mixture 
  is 
  rapidly 
  poured 
  over 
  the 
  glass 
  to 
  be 
  cooled. 
  In 
  

   five 
  or 
  six 
  minutes, 
  at 
  a 
  temperature 
  of 
  15° 
  to 
  19°, 
  all 
  the 
  silver 
  

   in 
  the 
  solution 
  is 
  deposited 
  in 
  a 
  brilliant 
  layer 
  which 
  can 
  then 
  be 
  

   washed 
  with 
  water. 
  — 
  Journal 
  de 
  Physique, 
  January, 
  1895. 
  

  

  J. 
  T. 
  

  

  9. 
  A 
  Form 
  of 
  Sensitive 
  Galvanometer. 
  — 
  In 
  a 
  note 
  to 
  the 
  

   French 
  Academy, 
  presented 
  by 
  Prof. 
  Mascart, 
  M. 
  Pierre 
  Weiss 
  

   describes 
  a 
  new 
  method 
  of 
  making 
  the 
  suspended 
  magnetic 
  

   system 
  of 
  a 
  galvanometer. 
  The 
  system 
  is 
  formed 
  of 
  long 
  

   vertical 
  needles, 
  placed 
  parallel 
  to 
  the 
  axis 
  of 
  rotation 
  in 
  such 
  a 
  

   manner 
  that 
  they 
  constitute 
  with 
  their 
  opposed 
  poles 
  almost 
  a 
  

   closed 
  magnetic 
  circuit. 
  Each 
  one 
  of 
  the 
  two 
  systems 
  of 
  poles 
  

   is 
  placed 
  at 
  the 
  center 
  of 
  suitably 
  constructed 
  bobbins. 
  The 
  

   almost 
  complete 
  absence 
  of 
  demagnetizing 
  force, 
  allows 
  the 
  

   maximum 
  magnetization 
  of 
  the 
  steel 
  : 
  and 
  one 
  can 
  by 
  changing 
  

   the 
  distance 
  of 
  the 
  needle 
  change 
  at 
  will 
  the 
  ratio 
  of 
  the 
  mag- 
  

   netic 
  moment 
  to 
  the 
  moment 
  of 
  inertia. 
  If 
  the 
  sensibility 
  of 
  a 
  

   galvanometer 
  is 
  defined 
  as 
  the 
  number 
  of 
  divisions 
  which 
  it 
  indi- 
  

   cates 
  for 
  one 
  micro-ampere 
  divided 
  by 
  the 
  square 
  root 
  of 
  the 
  

   resistance, 
  the 
  scale 
  being 
  at 
  a 
  distance 
  from 
  the 
  mirror 
  equal 
  to 
  

   2000 
  divisions 
  and 
  the 
  duration 
  of 
  the 
  oscillation 
  being 
  five 
  

   seconds, 
  M. 
  Weiss 
  obtains 
  S 
  = 
  1500. 
  This 
  sensibility 
  can 
  be 
  

   increased 
  by 
  greater 
  care 
  in 
  the 
  mechanical 
  construction 
  of 
  the 
  

   instrument. 
  The 
  author 
  states 
  that 
  Mr. 
  Wadsworth, 
  Phil. 
  Mag., 
  

   No. 
  38, 
  1894, 
  describes 
  a 
  galvanometer 
  of 
  more 
  difficult 
  construc- 
  

   tion 
  which 
  gave 
  S 
  = 
  1300. 
  — 
  Gomptes 
  Henclus, 
  No. 
  13, 
  April, 
  

   1895. 
  j. 
  t. 
  

  

  10. 
  On 
  the 
  Diselectrification 
  of 
  Air. 
  — 
  Lord 
  Kelvin 
  has 
  con- 
  

   tinued 
  his 
  experiments 
  on 
  this 
  subject 
  with 
  the 
  assistance 
  of 
  

   Messrs. 
  Magnus 
  Maclean 
  and 
  Alexander 
  Galt. 
  It 
  was 
  found 
  

   that 
  positive 
  or 
  negative 
  electricity 
  given 
  to 
  air 
  by 
  an 
  electrified 
  

   needle-point 
  can 
  be 
  conveyed 
  through 
  3 
  or 
  4 
  meters 
  of 
  small 
  

   metal 
  tube 
  (l 
  cm 
  diameter) 
  and 
  shown 
  on 
  a 
  quadrant 
  electrometer 
  

   by 
  a 
  receiving 
  filter. 
  A 
  filter 
  of 
  120 
  wire 
  gauges 
  only 
  reduced 
  

   the 
  electrical 
  indication 
  to 
  a 
  little 
  less 
  than 
  half 
  of 
  what 
  it 
  was 
  

  

  