﻿36 
  Rowland 
  and 
  Penniman 
  — 
  Electrical 
  Measurements. 
  

  

  time 
  of 
  5 
  of 
  these. 
  The 
  taking 
  of 
  the 
  speed 
  during 
  every 
  

   experiment 
  gave 
  more 
  regular 
  results, 
  as 
  the 
  speed 
  was 
  con- 
  

   stantly 
  changing, 
  the 
  dynamo 
  being 
  run 
  by 
  the 
  engine 
  in 
  the 
  

   University 
  power-house 
  when 
  it 
  was 
  subject 
  to 
  great 
  change 
  of 
  

   load. 
  This 
  dynamo 
  had 
  a 
  period 
  of 
  about 
  132 
  complete 
  periods 
  

   per 
  second. 
  

  

  For 
  the 
  production 
  of 
  a 
  current 
  of 
  less 
  period 
  than 
  that 
  of 
  

   the 
  Westinghouse, 
  the 
  small 
  alternator 
  constructed 
  at 
  the 
  

   University 
  was 
  used. 
  This 
  dynamo 
  was 
  run 
  by 
  a 
  small 
  con- 
  

   tinuous 
  Sprague 
  motor. 
  The 
  armature 
  of 
  the 
  small 
  alternator 
  

   consisted 
  of 
  8 
  coils, 
  which 
  coils 
  were 
  fastened 
  flat 
  on 
  a 
  german 
  

   silver 
  plate, 
  the 
  plate 
  revolving 
  between 
  8 
  field 
  pieces 
  produc- 
  

   ing 
  4 
  poles. 
  The 
  object 
  of 
  having 
  the 
  coils 
  of 
  the 
  armature 
  

   on 
  a 
  metal 
  plate 
  was 
  to 
  secure 
  a 
  nearly 
  constant 
  speed. 
  The 
  

   metal 
  plate 
  produced 
  a 
  load 
  that 
  varied 
  as 
  the 
  velocity 
  and 
  

   due 
  to 
  induced 
  currents 
  in 
  the 
  plate. 
  The 
  varying 
  load, 
  

   depending 
  on 
  the 
  velocity 
  of 
  the 
  moving 
  plate, 
  produced 
  

   a 
  nearly 
  constant 
  speed, 
  which 
  rendered 
  unnecessary 
  the 
  

   constant 
  taking 
  of 
  the 
  speed. 
  When 
  this 
  dynamo 
  was 
  used, 
  

   the 
  speedy 
  was 
  only 
  determined 
  two 
  or 
  three 
  times 
  during 
  

   a 
  series 
  of 
  readings 
  or 
  experiments. 
  The 
  average 
  of 
  these 
  

   determinations 
  was 
  taken 
  as 
  the 
  speed 
  during 
  the 
  whole 
  series 
  

   of 
  experiments 
  under 
  consideration. 
  

  

  Coils. 
  — 
  The 
  coils 
  whose 
  inductances 
  were 
  determined 
  were 
  

   all 
  made 
  in 
  the 
  same 
  way, 
  being 
  wound 
  on 
  a 
  metal 
  form 
  and 
  

   soaked 
  in 
  a 
  preparation 
  of 
  wax. 
  When 
  the 
  wax 
  was 
  hard 
  the 
  

   metal 
  form 
  was 
  removed. 
  This 
  enabled 
  the 
  coils 
  to 
  be 
  placed 
  

   close 
  together, 
  as 
  their 
  sides 
  were 
  fiat 
  and 
  smooth. 
  The 
  coils 
  

   all 
  had 
  the 
  same 
  internal 
  and 
  external 
  diameter, 
  but 
  their 
  width 
  

   varied, 
  that 
  being 
  determined 
  by 
  the 
  number 
  of 
  turns 
  that 
  

   were 
  desired. 
  

  

  Coils. 
  Pj. 
  External 
  diameter 
  35*46^"', 
  internal 
  diameter 
  

   23-8^% 
  was 
  made 
  up 
  of 
  about 
  1200 
  turns 
  of 
  JS'o. 
  16 
  B 
  and 
  S 
  

   gauge 
  single 
  covered 
  cotton 
  copper 
  wire, 
  roughly 
  wound 
  ; 
  the 
  

   turns 
  were 
  not 
  smooth; 
  self-inductance 
  as 
  finally 
  determined 
  

   •566 
  henry. 
  

  

  P^. 
  Same 
  dimensions. 
  Turns 
  were 
  put 
  on 
  evenly. 
  The 
  

   number 
  of 
  turns 
  was 
  1300 
  of 
  ]^o. 
  16 
  B 
  and 
  S 
  single 
  covered 
  

   cotton 
  copper 
  wire. 
  Self-inductance 
  '721 
  henry. 
  

  

  A. 
  Same 
  internal 
  and 
  external 
  diameters 
  as 
  P, 
  but 
  the 
  width 
  

   was 
  4-3^'". 
  Number 
  of 
  turns 
  3700 
  No. 
  20 
  B 
  and 
  S 
  gauge 
  single 
  

   covered 
  cotton 
  copper 
  wire. 
  Self-inductance 
  as 
  determined 
  

   6-30 
  henrys. 
  

  

  BjB^. 
  This 
  coil 
  was 
  made 
  by 
  winding 
  two 
  wires 
  in 
  parallel 
  

   and 
  all 
  four 
  of 
  the 
  terminals 
  brought 
  out 
  to 
  binding 
  posts. 
  

   Thus 
  the 
  coils 
  could 
  be 
  used 
  as 
  two 
  single 
  coils, 
  when 
  the 
  coils 
  

   will 
  be 
  denoted 
  by 
  the 
  symbols 
  B, 
  and 
  B^ 
  as 
  the 
  case 
  may 
  be, 
  

  

  