﻿756 
  Mr. 
  W. 
  A. 
  Jenkins 
  : 
  New 
  Method 
  of 
  Determining 
  the 
  

  

  before 
  "it 
  turned 
  round 
  the 
  tube. 
  Its 
  passing 
  through 
  two 
  

   wire 
  brushes 
  connected 
  with 
  an 
  electric 
  circuit 
  enabled 
  this 
  

   to 
  be 
  done. 
  

  

  As 
  it 
  was 
  not 
  desirable 
  to 
  leave 
  the 
  helix 
  open 
  to 
  the 
  

   atmosphere, 
  the 
  tube 
  was 
  coated 
  over 
  with 
  a 
  solution 
  of 
  

   shellac. 
  Best 
  shellac 
  was 
  dissolved 
  in 
  pure 
  methylated 
  

   spirits, 
  the 
  solution 
  filtered 
  twice 
  and 
  then 
  applied 
  to 
  the 
  

   tube. 
  Six 
  coatings 
  were 
  given, 
  and 
  each 
  one 
  was 
  allowed 
  to 
  

   dry 
  before 
  the 
  next 
  was 
  applied. 
  The 
  wires 
  could 
  easily 
  be 
  

   seen 
  through 
  the 
  transparent 
  shellac, 
  and 
  the 
  preceding- 
  

   experiment 
  of 
  determining 
  the 
  number 
  of 
  turns 
  per 
  cm. 
  was 
  

   easily 
  carried 
  out. 
  

  

  When 
  the 
  experiment 
  is 
  performed 
  the 
  current 
  sent 
  through 
  

   the 
  wire 
  is 
  about 
  *014 
  ampere 
  and, 
  as 
  will 
  be 
  seen 
  later, 
  no 
  

   appreciable 
  rise 
  in 
  temperature 
  due 
  to 
  the 
  passage 
  of 
  the 
  

   current 
  takes 
  place. 
  There 
  is 
  a 
  possibility 
  of 
  leakage 
  from 
  

   turn 
  to 
  turn 
  through 
  the 
  shellac, 
  but 
  as 
  the 
  latter 
  is 
  a 
  good 
  

   insulator 
  the 
  error 
  caused 
  by 
  this 
  is 
  insignificant. 
  # 
  

  

  Suspension 
  of 
  the 
  Magnet. 
  

  

  The 
  central 
  portion 
  of 
  the 
  tube 
  cannot 
  be 
  pierced 
  to 
  allow 
  

   of 
  a 
  silk 
  fibre 
  being 
  passed 
  through 
  it 
  owing 
  to 
  the 
  winding 
  

   being 
  thereby 
  made 
  uneven. 
  

  

  It 
  was 
  thought 
  that 
  it 
  might 
  be 
  possible 
  to 
  make 
  use 
  of 
  a 
  

   system 
  supported 
  by 
  a 
  needle 
  resting 
  with 
  its 
  point 
  on 
  a 
  

   polished 
  glass 
  surface, 
  but 
  it 
  was 
  found 
  that 
  however 
  fine 
  

   the 
  needle-point 
  was 
  and 
  however 
  much 
  the 
  surface 
  was 
  

   polished, 
  the 
  system 
  came 
  to 
  rest 
  after 
  about 
  8 
  minutes 
  and, 
  

   as 
  this 
  prevents 
  an 
  accurate 
  determination 
  of 
  its 
  period 
  of 
  

   oscillation 
  being 
  made, 
  silk 
  fibre 
  was 
  adopted. 
  The 
  whole 
  of 
  

   the 
  suspending 
  apparatus 
  must 
  be 
  inside 
  the 
  tube 
  and 
  this 
  

   necessitates 
  a 
  short 
  fibre 
  being 
  used. 
  The 
  internal 
  diameter 
  

   of 
  the 
  tube 
  is 
  only 
  4 
  cm., 
  so 
  that 
  the 
  length 
  of 
  the 
  fibre 
  is 
  

   limited 
  to 
  from 
  2 
  to 
  2*5 
  cm., 
  as 
  it 
  is 
  advisable 
  to 
  have 
  the 
  

   magnet 
  in 
  the 
  vicinity 
  of 
  the 
  axis 
  of 
  the 
  tube. 
  Further, 
  the 
  

   apparatus 
  must 
  be 
  provided 
  with 
  a 
  means 
  of 
  turning 
  the 
  fibre 
  

   round 
  through 
  180°, 
  in 
  order 
  that 
  the 
  alteration 
  in 
  torsion, 
  

   caused 
  by 
  the 
  reversing 
  of 
  the 
  magnet, 
  might 
  be 
  eliminated. 
  

   It 
  must 
  also 
  be 
  so 
  arranged 
  that 
  it 
  is 
  easy 
  to 
  take 
  the 
  

   suspending 
  apparatus 
  out 
  of 
  the 
  tube, 
  in 
  order 
  to 
  make 
  any 
  

   necessary 
  alterations, 
  such 
  as 
  the 
  replacing 
  of 
  a 
  silk 
  fibre. 
  

   The 
  suspended 
  magnet 
  must 
  also 
  carry 
  a 
  mirror, 
  by 
  means 
  of 
  

   which, 
  with 
  the 
  aid 
  of 
  an 
  optical 
  system, 
  the 
  determination 
  

   of 
  the 
  period 
  of 
  oscillation 
  can 
  be 
  made. 
  All 
  these 
  are 
  

   allowed 
  for 
  in 
  the 
  apparatus 
  finally 
  used, 
  diagrams 
  and 
  

   descriptions 
  of 
  which 
  follow. 
  

  

  