﻿of 
  the 
  Atomic 
  Weights 
  of 
  Elementary 
  Substances, 
  737 
  

  

  It 
  is 
  a 
  common 
  error 
  to 
  assume 
  that 
  discoverers 
  in 
  various 
  

   departments 
  of 
  science 
  are, 
  necessarily, 
  authorities 
  on 
  the 
  

   co-ordination 
  of 
  the 
  subject 
  of 
  their 
  discoveries 
  with 
  the 
  

   general 
  properties 
  of 
  bodies, 
  and 
  with 
  the 
  real 
  nature 
  of 
  

   things. 
  Thus 
  (1) 
  Peligot 
  adopted 
  120 
  as 
  the 
  atomic 
  weight 
  

   of 
  uranium, 
  and 
  Stromeyer 
  56 
  for 
  cadmium, 
  the 
  modern 
  

   determinations 
  for 
  these 
  elements 
  being 
  240 
  and 
  112 
  respec- 
  

   tively. 
  (2) 
  Scheele's 
  oxymuriatic 
  acid 
  was 
  shown 
  by 
  Davy 
  

   to 
  be 
  elementary 
  chlorine. 
  (3) 
  Platinum 
  was 
  identified 
  by 
  

   its 
  Brazilian 
  discoverer 
  with 
  silver, 
  and 
  derived 
  its 
  name 
  

   from 
  that 
  metal. 
  Many 
  similar 
  instances 
  may 
  be 
  adduced 
  

   from 
  other 
  departments 
  of 
  the 
  natural 
  sciences. 
  It 
  will 
  

   be 
  sufficient 
  to 
  mention 
  in 
  this 
  connexion 
  the 
  discovery 
  

   and 
  first 
  appearance 
  of 
  Saturn's 
  rings, 
  the 
  supposed 
  co- 
  

   metary 
  nature 
  of 
  the 
  planet 
  Uranus, 
  and 
  the 
  landfall 
  of 
  

   Columbus. 
  

  

  Helium, 
  as 
  will 
  be 
  seen 
  in 
  several 
  of 
  my 
  papers, 
  is 
  the 
  

   typical 
  element 
  of 
  the 
  series 
  H 
  2n, 
  with 
  an 
  atomic 
  weight 
  

   ot'2(He=2) 
  as 
  shown 
  in 
  the 
  following 
  table 
  (p. 
  738). 
  This 
  

   number 
  has 
  been 
  adopted 
  by 
  French 
  chemists 
  in 
  the 
  table 
  of 
  

   atomic 
  weights 
  published 
  in 
  the 
  Annuaire 
  die 
  Bureau 
  des 
  

   Longitudes. 
  

  

  Further 
  inspection 
  of 
  the 
  Table 
  will 
  show 
  that, 
  in 
  con- 
  

   sequence 
  of 
  the 
  law 
  of 
  multiple 
  proportions 
  by 
  which 
  the 
  

   atomic 
  weights 
  of 
  the 
  series 
  are 
  determined, 
  there 
  is 
  a 
  

   common 
  difference 
  of 
  23 
  between 
  the 
  atomic 
  weights 
  of 
  the 
  

   series 
  H?z 
  (commencing 
  with 
  K) 
  to 
  the 
  final 
  member 
  Hg. 
  

   In 
  like 
  manner 
  there 
  is 
  a 
  common 
  difference 
  of 
  24 
  in 
  the 
  

   strictly 
  parallel 
  series 
  H2h. 
  The 
  regular 
  parallel 
  differences 
  

   between 
  the 
  atomic 
  weights 
  of 
  members 
  at 
  the 
  head 
  of 
  both 
  

   series 
  are 
  equally 
  remarkable. 
  

  

  I 
  have 
  discussed 
  in 
  former 
  papers 
  the 
  alternation 
  of 
  light 
  

   and 
  heavy 
  metals 
  in 
  regular 
  order 
  observable 
  in 
  each 
  of 
  

   these 
  series, 
  and 
  have 
  put 
  forward 
  suggestions 
  as 
  to 
  its 
  

   possible 
  cause 
  in 
  my 
  first 
  papers 
  on 
  the 
  " 
  Origin 
  of 
  

   Elementary 
  Substances," 
  published 
  by 
  the 
  Society 
  in 
  1878 
  

   and 
  18«7. 
  

  

  Radium 
  (as 
  was 
  indicated 
  in 
  my 
  Table 
  of 
  Elements 
  some 
  

   years 
  previous 
  to 
  its 
  discovery) 
  is 
  one 
  of 
  the 
  synthetic 
  trans- 
  

   formations 
  of 
  helium 
  in 
  the 
  series 
  H2n, 
  and 
  is 
  the 
  next 
  

   higher 
  member 
  to 
  barium 
  of 
  the 
  alkaline-earth 
  metals. 
  This 
  

   place 
  has 
  since 
  been 
  assigned 
  to 
  radium 
  by 
  Mme. 
  Curie, 
  but 
  

   with 
  an 
  erroneous 
  atomic 
  weight 
  and 
  specific 
  gravity 
  ; 
  as 
  

   will 
  be 
  seen 
  by 
  comparison 
  with 
  the 
  similar 
  properties 
  of 
  the 
  

   other 
  members 
  of 
  the 
  same 
  series 
  (Philosophical 
  Magazine, 
  

   February 
  1908). 
  

  

  