﻿206 
  Drs. 
  Smeeth 
  and 
  Watson 
  on 
  the 
  Radioactivity 
  of 
  

  

  6. 
  Prof. 
  Plummer 
  appears 
  to 
  consider 
  it 
  a 
  mistake 
  to 
  

   regard 
  as 
  a 
  mass 
  the 
  mutual 
  induction 
  M 
  of 
  the 
  electrical 
  

   case. 
  

  

  But 
  does 
  not 
  the 
  current 
  view 
  regard 
  the 
  mutual 
  induc- 
  

   tion 
  as 
  an 
  inertia 
  factor 
  of 
  some 
  sort? 
  Thus 
  in 
  Sir 
  J. 
  J. 
  

   Thomson's 
  model 
  referred 
  to 
  in 
  the 
  October 
  paper 
  (p. 
  251) 
  

   both 
  self 
  and 
  mutual 
  inductions 
  are 
  represented 
  by 
  masses. 
  

   In 
  Prof. 
  J. 
  A. 
  Fleming's 
  ' 
  Alternate 
  Current 
  Transformer 
  ' 
  

   (vol. 
  i. 
  pp. 
  97-98, 
  1889), 
  the 
  electrical 
  energy 
  -JLi 
  2 
  is 
  

   likened 
  to 
  the 
  mechanical 
  energy 
  of 
  rotation 
  ^Io> 
  2 
  . 
  Again, 
  

   in 
  Sir 
  Oliver 
  Lodge's 
  ' 
  Modern 
  Views 
  of 
  Electricity 
  ' 
  (p. 
  496, 
  

   1907), 
  coefficient 
  of 
  induction 
  (self 
  or 
  mutual) 
  is 
  given 
  as 
  

   inertia 
  per 
  unit 
  area. 
  

  

  It 
  is 
  true 
  that 
  the 
  coupling 
  in 
  the 
  electrical 
  case 
  is 
  made 
  

   by 
  a 
  change 
  of 
  configuration 
  which 
  fixes 
  the 
  value 
  of 
  M. 
  

   But 
  this 
  does 
  not 
  prevent 
  M 
  from 
  being 
  a 
  mass 
  (i. 
  e., 
  an 
  

   inertia) 
  like 
  the 
  inductances 
  L 
  and 
  N 
  which 
  are 
  also 
  

   dependent 
  solely 
  on 
  configurations, 
  provided 
  no 
  iron 
  or 
  

   other 
  magnetizable 
  substances 
  are 
  present. 
  As 
  to 
  whether 
  

   the 
  coefficient 
  M 
  in 
  the 
  electrical 
  equations 
  is 
  to 
  be 
  repre- 
  

   sented 
  by 
  a 
  mass 
  in 
  any 
  one 
  mechanical 
  model 
  incompletely 
  

   analogous 
  to 
  it, 
  is 
  another 
  matter. 
  

  

  Nottingham, 
  

   Dec. 
  17, 
  1917. 
  

  

  XXIII. 
  The 
  Radioactivity 
  of 
  Archazan 
  Rocks 
  from 
  the 
  Mysore 
  

   State, 
  South 
  India. 
  ByW. 
  F. 
  Smeeth, 
  D.Sc, 
  A.R.S.M., 
  

   and 
  H. 
  E. 
  Watson, 
  D.Sc, 
  A.I.C.* 
  

  

  Preliminary 
  Investigation. 
  

  

  THIS 
  investigation 
  was 
  started 
  some 
  years 
  ago 
  on 
  a 
  

   number 
  of 
  samples 
  of 
  the 
  hornblendic 
  schists 
  of 
  the 
  

   Kolar 
  Gold 
  Field, 
  selected 
  by 
  Mr. 
  H. 
  M. 
  A. 
  Cooke, 
  Super- 
  

   intendent 
  of 
  the 
  Ooregum 
  Gold 
  Mining 
  Company. 
  

  

  The 
  samples 
  were 
  taken 
  from 
  the 
  Kolar 
  mines 
  at 
  different 
  

   depths, 
  with 
  a 
  view 
  to 
  ascertaining 
  whether 
  the 
  radium 
  con- 
  

   tent 
  varied 
  with 
  the 
  depth 
  from 
  the 
  surface 
  in 
  rock 
  of 
  fairly 
  

   uniform 
  character 
  and 
  composition. 
  These 
  hornblendic 
  

   schists 
  and 
  epidiorites 
  are 
  all 
  ancient 
  lava 
  flows, 
  or 
  sills, 
  of 
  

   fairly 
  uniform 
  composition, 
  notwithstanding 
  petrological 
  dis- 
  

   tinctions 
  in 
  texture 
  and 
  structure. 
  

  

  * 
  Communicated 
  by 
  the 
  Authors. 
  

  

  