﻿Rotoland 
  and 
  Penniman 
  — 
  Electrical 
  Measitrements. 
  35 
  

  

  Art. 
  YL 
  — 
  Electrical 
  Measurements; 
  by 
  Henry 
  A. 
  

   Rowland 
  and 
  Thomas 
  Dobbin 
  Penniman.^ 
  

  

  In 
  a 
  previous 
  articlef 
  mention 
  was 
  made 
  of 
  some 
  work 
  

   then 
  being 
  carried 
  on 
  at 
  the 
  Johns 
  Hopkins 
  University 
  to 
  test 
  

   tlie 
  methods 
  for 
  the 
  measurement 
  and 
  comparison 
  of 
  self- 
  

   inductance, 
  mutual 
  inductance, 
  and 
  capacity 
  there 
  described. 
  

  

  In 
  the 
  present 
  paper, 
  there 
  will 
  be 
  given 
  an 
  account 
  of 
  the 
  

   experiments 
  performed 
  with 
  some 
  of 
  the 
  methods 
  described 
  in 
  

   the 
  previous 
  article, 
  together 
  with 
  a 
  method 
  for 
  the 
  direct 
  

   measurement 
  of 
  the 
  effect 
  of 
  electric 
  absorption 
  in 
  terms 
  of 
  

   resistance. 
  

  

  The 
  methods 
  that 
  were 
  tried 
  were 
  25, 
  26, 
  9, 
  3, 
  12 
  and 
  6. 
  

  

  Apparatus, 
  

  

  Description 
  of 
  the 
  electrodynamometer^ 
  dynamos, 
  coils, 
  condensers, 
  

   resistances 
  and 
  connections 
  used 
  in 
  the 
  experiments. 
  

  

  Electrodynamometer. 
  — 
  The 
  electrodynamometer 
  'was 
  one 
  

   constructed 
  at 
  the 
  University, 
  having 
  a 
  sensitiveness, 
  with 
  the 
  

   coils 
  in 
  series, 
  of 
  1 
  scale 
  division 
  deflection 
  for 
  -0007 
  ampere. 
  

  

  The 
  hanging 
  coil 
  was 
  made 
  up 
  of 
  240 
  turns 
  of 
  I^o. 
  34 
  cop- 
  

   per 
  wire 
  B 
  and 
  S 
  gauge. 
  The 
  coil 
  was 
  suspended 
  by 
  a 
  bronze 
  

   wire 
  connected 
  with 
  one 
  terminal 
  of 
  the 
  coil. 
  The 
  other 
  

   terminal 
  of 
  the 
  coil 
  was 
  a 
  loop 
  of 
  wire 
  hanging 
  from 
  the 
  bot- 
  

   tom 
  of 
  the 
  coil 
  and 
  attached 
  to 
  the 
  side 
  of 
  the 
  case 
  ; 
  both 
  the 
  

   suspension 
  and 
  the 
  loop 
  were 
  brought 
  out 
  to 
  binding 
  posts. 
  

   The 
  resistance 
  of 
  the 
  coil 
  with 
  suspension 
  was 
  21*7 
  ohms. 
  

  

  The 
  fixed 
  coils 
  were 
  made 
  up 
  of 
  300 
  turns 
  each 
  of 
  No. 
  30 
  B 
  

   and 
  S 
  gauge 
  copper 
  wire. 
  The 
  coils 
  were 
  wound 
  on 
  cup- 
  

   shaped 
  metal 
  forms 
  and 
  soaked 
  in 
  a 
  preparation 
  of 
  wax. 
  The 
  

   form 
  was 
  then 
  removed 
  and 
  the 
  coils 
  placed 
  a 
  radius 
  apart 
  as 
  

   in 
  the 
  arrangement 
  of 
  Helmholtz. 
  

  

  Dynamos. 
  — 
  There 
  were 
  two 
  dynamos 
  used, 
  a 
  Westinghouse 
  

   alternator, 
  and 
  a 
  small 
  alternating 
  dynamo 
  constructed 
  at 
  the 
  

   University. 
  The 
  Westinghouse 
  dynamo 
  was 
  one 
  having 
  10 
  

   poles 
  so 
  that 
  each 
  revolution 
  of 
  the 
  armature 
  produced 
  5 
  com- 
  

   plete 
  periods. 
  The 
  period 
  of 
  this 
  dynamo 
  was 
  determined 
  

   by 
  taking 
  the 
  time 
  of 
  1000 
  revolutions 
  of 
  the 
  armature. 
  This 
  

   was 
  accomplished 
  by 
  having 
  the 
  armature 
  make 
  an 
  electric 
  

   connection 
  with 
  a 
  bell 
  every 
  200 
  revolutions 
  and 
  taking 
  the 
  

  

  *This 
  Journal, 
  iv, 
  p. 
  429, 
  December, 
  1S9T; 
  Philosophical 
  Magazine. 
  January, 
  

   1898. 
  

  

  f 
  Abstract 
  of 
  Thesis 
  for 
  the 
  degree 
  of 
  Ph.D. 
  

  

  