﻿760 
  Mr. 
  W. 
  A. 
  Jenkins 
  : 
  JSew 
  Method 
  of 
  Determining 
  the 
  

  

  Thus 
  on 
  withdrawing 
  the 
  screw 
  K, 
  the 
  board 
  is 
  pulled 
  back 
  

   and 
  kept 
  tightly 
  pressed 
  against 
  the 
  point 
  of 
  the 
  screw. 
  

  

  The 
  final 
  adjusting 
  of 
  the 
  position 
  of 
  the 
  solenoid 
  so 
  that 
  

   it 
  lies 
  exactly 
  parallel 
  to 
  the 
  earth's 
  field, 
  is 
  performed 
  as 
  

   follows. 
  Adjust 
  the 
  optical 
  system 
  until 
  the 
  image 
  of 
  the 
  

   filament 
  of 
  the 
  Nernst 
  lamp 
  is 
  coincident 
  with 
  the 
  inter- 
  

   section 
  of 
  the 
  cross- 
  wires 
  of 
  the 
  telescope. 
  Send 
  a 
  current 
  

   round 
  the 
  solenoid 
  so 
  as 
  to 
  produce 
  a 
  field, 
  parallel 
  to, 
  and 
  

   in 
  the 
  same 
  direction 
  as 
  that 
  of 
  the 
  earth. 
  If 
  now 
  the 
  

   solenoid 
  be 
  slightly 
  out 
  of 
  its 
  correct 
  position 
  the 
  magnet 
  

   will 
  be 
  deflected, 
  and 
  the 
  image 
  of 
  the 
  filament 
  will 
  no 
  

   longer 
  coincide 
  with 
  the 
  intersection 
  of 
  the 
  cross-wires 
  of 
  

   the 
  telescope. 
  If 
  such 
  be 
  the 
  case, 
  rotate 
  the 
  solenoid 
  until, 
  

   on 
  sending 
  a 
  current 
  through 
  the 
  coil, 
  no 
  deflexion 
  of 
  the 
  

   magnet 
  occurs. 
  By 
  then 
  sending 
  a 
  large 
  current 
  momen- 
  

   tarily 
  round 
  the 
  solenoid 
  a 
  very 
  delicate 
  adjustment 
  of 
  the 
  

   position 
  of 
  the 
  magnet 
  can 
  be 
  made. 
  

  

  Electrical 
  arrangement 
  for 
  sending 
  and 
  measuring 
  

   the 
  Current 
  through 
  the 
  Solenoid. 
  

  

  fear. 
  3. 
  

  

  G, 
  

  

  G, 
  

  

  kvWAV/AVVAV.MA 
  JWUVVTOVAVWH 
  

  

  S 
  I 
  

  

  The 
  lower 
  half 
  of 
  fig. 
  3 
  depicts 
  the 
  apparatus 
  used 
  for 
  

   sending 
  and 
  adjusting 
  the 
  current 
  round 
  the 
  solenoid. 
  A 
  two- 
  

   volt 
  storage-cell 
  E 
  supplies 
  the 
  current 
  which 
  passes 
  through 
  

   a 
  resistance-box 
  R, 
  a 
  low 
  resistance 
  wire 
  D, 
  round 
  the 
  

   solenoid, 
  and 
  through 
  the 
  standard 
  10 
  ohms 
  resistance 
  S. 
  

   'The 
  solenoid 
  is 
  connected 
  to 
  the 
  low-resistance 
  wire 
  D 
  by 
  

  

  