﻿504 
  Dr. 
  W. 
  Mansergh 
  Varley 
  on 
  Magnetism 
  induced 
  

  

  kept 
  unaltered 
  throughout 
  a 
  whole 
  series 
  of 
  measurements. 
  

   The 
  direction 
  of 
  the 
  current 
  through 
  one 
  of 
  the 
  coils 
  (L 
  3 
  ) 
  

   could 
  be 
  reversed 
  by 
  means 
  of 
  the 
  commutator 
  (K), 
  so 
  that 
  

   the 
  coils 
  acted 
  in 
  the 
  same 
  or 
  in 
  opposite 
  senses 
  on 
  the 
  cathode- 
  

   rays. 
  A 
  few 
  less 
  important 
  precautions 
  must 
  also 
  be 
  taken 
  

   in 
  arranging 
  the 
  apparatus. 
  

  

  A 
  scale 
  cut 
  in 
  tinfoil, 
  on 
  glass, 
  strongly 
  illumined 
  from 
  

   behind, 
  was 
  projected 
  on 
  to 
  the 
  screen 
  of 
  the 
  Braun's 
  tube, 
  

   the 
  lenses 
  being 
  arranged 
  so 
  as 
  to 
  give 
  exactly 
  millimetre 
  

   divisions 
  on 
  the 
  screen, 
  this 
  arrangement 
  enabling 
  the 
  de- 
  

   flexions 
  to 
  be 
  read 
  with 
  the 
  utmost 
  accuracy 
  and 
  ease 
  in 
  the 
  

   perfectly 
  dark 
  room. 
  

  

  In 
  order 
  to 
  eliminate 
  the 
  electrostatic 
  effect 
  of 
  the 
  solenoids 
  

   acting 
  as 
  small 
  capacities, 
  the 
  tube 
  was 
  surrounded 
  by 
  a 
  layer 
  

   of 
  tinfoil 
  in 
  the 
  neighbourhood 
  of 
  the 
  solenoids. 
  

  

  4. 
  The 
  iron 
  wires 
  investigated 
  were 
  placed 
  as 
  evenly 
  as 
  

   possible 
  in 
  glass 
  tubes 
  of 
  such 
  a 
  diameter 
  as 
  to 
  slide 
  easily 
  in 
  

   and 
  out 
  of 
  the 
  cores 
  of 
  the 
  solenoids. 
  Each 
  wire 
  was 
  per- 
  

   fectly 
  insulated 
  from 
  the 
  others 
  in 
  the 
  same 
  bundle 
  by 
  being 
  

   coated 
  with 
  paraffin 
  or 
  shellac. 
  The 
  particulars 
  of 
  the 
  wires 
  

   used 
  in 
  four 
  of 
  the 
  bundles 
  are 
  given 
  in 
  the 
  following 
  table, 
  

   where 
  N 
  is 
  the 
  number 
  of 
  wires 
  in 
  the 
  bundle, 
  d 
  the 
  diameter 
  

   of 
  the 
  wire, 
  a 
  the 
  total 
  cross 
  section 
  of 
  the 
  wires 
  in 
  the 
  

   bundle, 
  and 
  S 
  the 
  whole 
  surface 
  of 
  the 
  wire 
  divided 
  by 
  the 
  

   length. 
  The 
  length 
  of 
  each 
  wire 
  was 
  9*0 
  cms. 
  

  

  Table 
  I. 
  

  

  Bundle. 
  

  

  N. 
  

  

  d, 
  cms. 
  

  

  a, 
  cm 
  2 
  . 
  

  

  S, 
  cms. 
  

  

  A 
  

  

  20 
  

  

  37 
  

  

  70 
  

  

  409 
  

  

  0100 
  

   0-071 
  

   0-0525 
  

  

  0157 
  

   0-147 
  

   0-152 
  

  

  6-28 
  

  

  8-25 
  

  

  11-54 
  

  

  28-4 
  

  

  B 
  

  

  c 
  

  

  D 
  

  

  00221 
  0-157 
  

  

  

  

  

  The 
  iron 
  wires 
  in 
  each 
  of 
  these 
  four 
  bundles 
  were 
  from 
  the 
  

   same 
  kind 
  of 
  iron, 
  and 
  kindly 
  placed 
  at 
  our 
  disposal 
  by 
  

   Messrs. 
  Siemens 
  & 
  Halske. 
  As 
  the 
  figures 
  show, 
  the 
  cross 
  

   section 
  in 
  each 
  of 
  the 
  four 
  bundles 
  was 
  nearly 
  the 
  same, 
  and 
  

   it 
  was 
  found, 
  on 
  placing 
  the 
  bundles 
  in 
  the 
  same 
  direct- 
  

   current 
  field, 
  that 
  the 
  induced 
  magnetization 
  in 
  each 
  was 
  also 
  

   very 
  nearly 
  equal, 
  thus 
  affording 
  a 
  suitable 
  series 
  to 
  test 
  the 
  

   influence 
  of 
  the 
  diameter 
  on 
  the 
  magnetization 
  in 
  an 
  oscil- 
  

   lating 
  electrical 
  field. 
  

  

  