﻿Horizontal 
  Intensity 
  of 
  the 
  Earth's 
  Magnetic 
  Field. 
  757 
  

  

  Fig. 
  1 
  shows 
  a 
  vertical 
  section 
  of 
  the 
  apparatus 
  supporting 
  

   the 
  magnet. 
  

  

  Fig. 
  1. 
  

  

  ^m 
  

  

  j 
  

  

  A 
  is 
  a 
  thin 
  brass 
  rod 
  to 
  which 
  the 
  two 
  split 
  brass 
  rings 
  B 
  

   and 
  B' 
  are 
  brazed. 
  These 
  two 
  split 
  rings 
  being 
  elastic, 
  serve 
  

   the 
  purpose 
  of 
  fitting 
  the 
  apparatus 
  firmly 
  to 
  the 
  inside 
  of 
  

   the 
  solenoid 
  tube. 
  C 
  is 
  a 
  small 
  circular 
  hole 
  midway 
  between 
  

   the 
  rings, 
  and 
  into 
  this 
  hole 
  the 
  actual 
  suspending 
  apparatus 
  

   D 
  fits. 
  D 
  is 
  a 
  piece 
  of 
  metal 
  fitting 
  into 
  the 
  circular 
  hole, 
  

   as 
  shown, 
  so 
  as 
  to 
  permit 
  of 
  easy 
  rotation. 
  The 
  pulley- 
  

   wheel 
  E 
  is 
  attached 
  rigidly 
  to 
  D, 
  and 
  through 
  both 
  D 
  and 
  E 
  

   a 
  fine 
  hole 
  passes. 
  The 
  silk 
  fibre 
  passes 
  through 
  this 
  hole 
  

   and 
  carries 
  the 
  magnet 
  F 
  and 
  mirror 
  G. 
  To 
  fasten 
  the 
  silk 
  

   fibre 
  a 
  little 
  melted 
  wax 
  was 
  poured 
  on 
  the 
  top 
  of 
  D, 
  when 
  

   the 
  fibre 
  had 
  been 
  threaded 
  through 
  the 
  hole 
  and 
  adjusted 
  to 
  

   its 
  proper 
  length. 
  

  

  x\t 
  the 
  end 
  of 
  the 
  brass 
  rod 
  remote 
  from 
  the 
  split 
  rings 
  is 
  

   a 
  narrow 
  slot 
  through 
  which 
  the 
  mechanism 
  JH 
  passes. 
  H 
  is 
  

   a 
  pulley-wheel 
  which 
  by 
  the 
  screwing 
  down 
  of 
  J 
  can 
  be 
  

   clamped 
  tightly 
  to 
  the 
  rod. 
  

  

  An 
  endless 
  cord 
  K 
  passes 
  round 
  the 
  two 
  pulley-wheels, 
  

   and 
  is 
  kept 
  taut 
  by 
  adjusting 
  the 
  position 
  of 
  the 
  wheel 
  H. 
  

   The 
  length 
  of 
  the 
  apparatus 
  is 
  such 
  that 
  when 
  the 
  magnet 
  is 
  

   at 
  the 
  centre 
  of 
  the 
  helix 
  the 
  pulley-wheel 
  H, 
  and 
  the 
  whole 
  

   of 
  the 
  slot 
  in 
  which 
  it 
  can 
  be 
  moved, 
  are 
  outside 
  the 
  solenoid. 
  

   When 
  the 
  cord 
  K 
  is 
  taut, 
  the 
  silk 
  fibre 
  suspension-head 
  can 
  

   be 
  rotated 
  by 
  turning 
  the 
  pulley-wheel 
  H. 
  A 
  definite 
  

   amount 
  of 
  torsion 
  can 
  therefore 
  be 
  taken 
  away 
  from 
  or 
  im- 
  

   parted 
  to 
  the 
  fibre 
  at 
  any 
  time. 
  

  

  The 
  Magnet 
  and 
  its 
  attachment 
  to 
  the 
  Fibre. 
  

  

  The 
  magnet 
  itself 
  consisted 
  of 
  several 
  pieces 
  of 
  magnetized 
  

   clock-spring 
  about 
  2'8 
  cm. 
  long 
  and 
  *25 
  cm. 
  wide. 
  These 
  

   pieces 
  of 
  clock-spring 
  fitted 
  into 
  a 
  light 
  aluminium 
  holder 
  

   to 
  the 
  upper 
  surface 
  of 
  which 
  the 
  silk 
  fibre 
  was 
  fastened 
  by 
  

   means 
  of 
  wax. 
  A 
  little 
  manipulation 
  was 
  necessary 
  in 
  order 
  

   to 
  o-et 
  the 
  fibre 
  attached 
  directly 
  above 
  the 
  centre 
  of 
  gravity 
  

   of 
  the 
  holder. 
  

  

  Phil 
  Mag. 
  S. 
  6. 
  Vol. 
  26. 
  No. 
  154. 
  Oct. 
  1913. 
  3 
  E 
  

  

  