﻿380 
  Webster 
  — 
  Producing 
  a 
  Constant 
  Angular 
  velocity. 
  

  

  Upon 
  the 
  shaft 
  of 
  a 
  continuous 
  current 
  motor, 
  M, 
  are 
  car- 
  

   ried 
  two 
  armatures, 
  one 
  for 
  the 
  main 
  driving 
  current, 
  the 
  

   other, 
  consisting 
  of 
  a 
  continuous 
  winding 
  with 
  collecting 
  rings, 
  

   for 
  the 
  auxiliary 
  regulating 
  current. 
  In 
  the 
  motor 
  generally 
  

   used 
  by 
  the 
  writer 
  for 
  this 
  purpose, 
  and 
  intended 
  for 
  about 
  

   one 
  horse-power, 
  the 
  two 
  armature 
  windings 
  are 
  wound 
  one 
  

   over 
  the 
  other, 
  and 
  are 
  in 
  the 
  same 
  field. 
  This 
  is 
  more 
  com- 
  

   pact 
  than 
  if 
  two 
  motors 
  are 
  connected 
  together, 
  and 
  somewhat 
  

   more 
  convenient 
  than 
  if 
  the 
  second 
  armature 
  is 
  replaced 
  by 
  

   ring 
  connections 
  at 
  two 
  points 
  in 
  the 
  main 
  armature, 
  which 
  is 
  

   simpler. 
  F 
  is 
  the 
  controlling 
  tuning 
  fork, 
  independently 
  

   driven 
  by 
  a 
  single 
  storage 
  cell. 
  The 
  auxiliary 
  current, 
  fur- 
  

   nished 
  by 
  the 
  storage-battery 
  A, 
  is 
  led 
  into 
  the 
  tuning-fork, 
  

   through 
  a 
  platinum 
  wire 
  carried 
  on 
  one 
  prong 
  to 
  a 
  mercury 
  

   break 
  B, 
  described 
  in 
  the 
  next 
  article, 
  and 
  then 
  through 
  a 
  

   switch 
  K 
  to 
  the 
  brushes 
  of 
  the 
  auxiliary 
  armature. 
  The 
  syn- 
  

   chronism 
  is 
  attained 
  by 
  means 
  of 
  the 
  following 
  arrangement. 
  

   A 
  mirror 
  carried 
  on 
  one 
  prong 
  of 
  the 
  fork 
  forms, 
  by 
  means 
  of 
  

   a 
  lens 
  L, 
  an 
  image 
  of 
  the 
  filament 
  of 
  an 
  incandescent 
  lamp 
  I, 
  

   whose 
  plane 
  is 
  horizontal, 
  on 
  a 
  screen 
  S. 
  This 
  screen 
  has 
  a 
  

   narrow 
  horizontal 
  slit, 
  which 
  allows 
  the 
  beam 
  of 
  light 
  to 
  pass 
  

   when 
  the 
  fork 
  is 
  nearly, 
  but 
  not 
  exactly, 
  in 
  its 
  equilibrium 
  

   position. 
  The 
  beam 
  then 
  passes 
  through 
  a 
  hole 
  in 
  a 
  screen 
  C, 
  

   and 
  being 
  reflected 
  from 
  the 
  mirror 
  R, 
  set 
  obliquely 
  on 
  the 
  

   shaft 
  of 
  the 
  motor, 
  forms 
  by 
  means 
  of 
  the 
  lens 
  1/ 
  a 
  small 
  

   bright 
  image 
  on 
  the 
  other 
  side 
  of 
  the 
  screen 
  C. 
  If 
  the 
  fork 
  is 
  

   at 
  rest 
  and 
  the 
  motor 
  revolving, 
  of 
  course 
  this 
  spot 
  is 
  drawn 
  

   out 
  into 
  a 
  bright 
  circle. 
  If 
  now 
  the 
  fork 
  be 
  set 
  in 
  motion, 
  

   the 
  beam 
  of 
  light 
  is 
  interrupted, 
  and 
  the 
  circle 
  is 
  broken 
  up 
  

   into 
  a 
  large 
  number 
  of 
  bright 
  arcs, 
  which 
  revolve 
  in 
  one 
  direc- 
  

   tion 
  or 
  the 
  other, 
  according 
  to 
  circumstances. 
  As 
  the 
  speed 
  of 
  

   the 
  motor 
  increases, 
  the 
  number 
  of 
  arcs 
  is 
  successively 
  reduced, 
  

   until 
  finally 
  there 
  are 
  only 
  two, 
  when 
  synchronism 
  is 
  nearly 
  

   attained. 
  The 
  two 
  arcs 
  move 
  first 
  in 
  the 
  reverse 
  direction 
  to 
  

   that 
  of 
  the 
  motor, 
  and 
  as 
  the 
  speed 
  increases, 
  finally 
  stand 
  

   still, 
  and 
  then 
  begin 
  to 
  move 
  in 
  the 
  direct 
  sense. 
  By 
  regulat- 
  

   ing 
  the 
  resistance 
  in 
  the 
  field 
  magnets 
  of 
  the 
  motor, 
  the 
  spots 
  

   may 
  be 
  made 
  to 
  stand 
  still. 
  We 
  then 
  have 
  a 
  convenient 
  stro- 
  

   boscope 
  method 
  suitable 
  for 
  regulation 
  by 
  hand 
  in 
  the 
  ordi- 
  

   nary 
  manner. 
  If 
  at 
  this 
  point 
  the 
  auxiliary 
  current 
  is 
  thrown 
  

   on 
  by 
  the 
  switch 
  K, 
  the 
  regulation 
  goes 
  on 
  of 
  itself, 
  and 
  if 
  the 
  

   auxiliary 
  current 
  has 
  been 
  made 
  of 
  the 
  proper 
  strength, 
  with- 
  

   out 
  further 
  attention. 
  Any 
  fluctuations 
  are 
  shown 
  by 
  the 
  

   oscillations 
  of 
  the 
  two 
  arcs 
  about 
  their 
  mean 
  positions, 
  and 
  by 
  

   measuring 
  the 
  angle 
  of 
  oscillation 
  and 
  the 
  time 
  in 
  which 
  it 
  is 
  

   performed, 
  the 
  variation 
  from 
  constancy 
  of 
  the 
  angular 
  veloc- 
  

   ity 
  may 
  be 
  determined. 
  Of 
  course 
  the 
  mean 
  angular 
  velocity 
  

  

  