﻿918 
  Prof. 
  Bragg 
  an 
  d 
  ]\i 
  r 
  . 
  Madsen 
  : 
  An 
  Experimental 
  

  

  Wi=[W 
  2 
  + 
  (27mL,) 
  2 
  ]*, 
  surpasses 
  by 
  about 
  25 
  percent, 
  at 
  

   the 
  most 
  the 
  simple 
  resistance, 
  W. 
  

  

  Combination 
  of 
  several 
  of 
  these 
  inductors 
  with 
  variously 
  

   directed 
  axes 
  is 
  evidently 
  possible 
  in 
  the 
  simplest 
  manner 
  ; 
  

   thence 
  also 
  the 
  determination 
  of 
  the 
  ratio 
  of 
  the 
  magnetic 
  

   components 
  to 
  the 
  total 
  field, 
  the 
  inclination, 
  &c. 
  

  

  A 
  special 
  case 
  arises, 
  if 
  the 
  middle 
  plane 
  of 
  the 
  windings 
  

   of 
  the 
  inductor-coil 
  is 
  placed 
  parallel 
  to 
  the 
  axis 
  of 
  y 
  instead 
  

   of 
  normal 
  to 
  it. 
  

  

  In 
  all 
  measurement- 
  with 
  the 
  earth 
  inductor 
  by 
  a 
  null 
  

   method 
  (adjusting 
  for 
  the 
  vanishing 
  of 
  the 
  induced 
  current) 
  

   it 
  is 
  most 
  effective 
  to 
  employ 
  as 
  indicator 
  a 
  resonance- 
  

   instrument 
  (string 
  galvanometer 
  or 
  the 
  like), 
  whose 
  own 
  

   frequency 
  lies 
  within 
  the 
  range 
  of 
  the 
  frequency 
  of 
  the 
  in- 
  

   ductor 
  (after 
  paying 
  due 
  regard 
  to 
  the 
  electromagnetic 
  

   constants 
  of 
  the 
  entire 
  circuit) 
  because 
  it 
  means 
  such 
  a 
  very 
  

   great 
  Increase 
  in 
  the 
  sharpness 
  of 
  the 
  observations. 
  A 
  re- 
  

   sonance 
  galvanometer, 
  /'. 
  /'., 
  indicating 
  currents 
  of 
  10~ 
  12 
  

   ampere 
  (I) 
  in 
  a 
  circuit 
  of 
  KM 
  ohm 
  total 
  resistance 
  (W) 
  

   shows 
  at 
  105 
  rotation- 
  per 
  minute 
  (60w) 
  the 
  presence 
  of 
  a 
  

   magnetic 
  field 
  F 
  = 
  5698 
  -1 
  . 
  KV'I/t-^Y 
  = 
  10 
  -6 
  gauss 
  rising 
  

   already 
  at 
  BUch 
  a 
  small 
  variation 
  of 
  the 
  earth-inductor's 
  

   axis 
  ./• 
  from 
  the 
  axis 
  of 
  the 
  geomagnetic 
  field, 
  that 
  the 
  angle 
  

   will 
  never 
  be 
  larger 
  than 
  that 
  caused 
  by 
  a 
  very 
  small 
  play 
  

   of 
  the 
  rotating 
  axis 
  in 
  its 
  bearings. 
  

  

  Degerloch, 
  AYuerttemberrr, 
  May 
  28, 
  1908. 
  

  

  LXXVIII. 
  An 
  Experimental 
  Investigation 
  of 
  the 
  Nature 
  of 
  

   y 
  Rays.—So. 
  2. 
  By 
  W. 
  H. 
  Bragg, 
  M.A., 
  F.R.S., 
  Elder 
  

   Professor 
  of 
  Mathematics 
  and 
  Physics 
  in 
  the 
  University 
  of 
  

   Adelaide 
  ; 
  and 
  J. 
  P. 
  V. 
  MADSEN, 
  U.Sc, 
  Lecturer 
  on 
  

   Electrical 
  Engineering 
  *. 
  

  

  TN 
  a 
  previous 
  paper 
  (Trans. 
  Boy. 
  Soc. 
  of 
  S.A. 
  1908, 
  p. 
  1) 
  

   we 
  have 
  given 
  a 
  preliminary 
  account 
  of 
  an 
  investigation 
  

   of 
  the 
  properties 
  of 
  the 
  secondary 
  radiation 
  due 
  to 
  7 
  rays, 
  and 
  

   discussed 
  the 
  evidence 
  thus 
  afforded 
  as 
  to 
  the 
  nature 
  of 
  the 
  

   rays. 
  The 
  first 
  section 
  of 
  the 
  present 
  paper 
  contains 
  an 
  

   account 
  of 
  further 
  experiments, 
  and 
  the 
  second 
  a 
  list 
  of 
  the 
  

   properties 
  of 
  the 
  secondary 
  radiation, 
  derived 
  in 
  part 
  from 
  

   the 
  work 
  of 
  other 
  observers, 
  and 
  in 
  part 
  from 
  our 
  own. 
  

   In 
  the 
  third 
  we 
  have 
  tried 
  to 
  show 
  that 
  the 
  properties 
  are 
  

  

  * 
  Communicated 
  by 
  the 
  Authors. 
  From 
  ' 
  Transactions 
  cf 
  the 
  Royal 
  

   Society 
  of 
  South 
  Australia/ 
  vol. 
  xxxii. 
  (1908). 
  

  

  