﻿134 
  

  

  Dr. 
  C. 
  V. 
  Drysdale 
  : 
  Rotes 
  

  

  Table 
  I. 
  

  

  Readings 
  on 
  Wrought 
  Iron 
  Ring. 
  

  

  Hole 
  

  

  No. 
  

  

  Fit. 
  

  

  H=30. 
  

  

  B. 
  

  

  H=1U0. 
  

  

  B. 
  

  

  1 
  

  

  Fair. 
  

  

  13,140 
  

  

  15,600 
  

  

  2 
  

  

  Moderate. 
  

  

  12.880 
  

  

  15.820 
  

  

  a 
  

  

  Good. 
  

  

  12,400 
  

  

  15,130 
  

  

  4 
  

  

  Good. 
  

  

  12,040 
  

  

  14.550 
  

  

  5 
  

  

  Fair. 
  

  

  11,730 
  

  

  14,550 
  

  

  6 
  

  

  Good. 
  

  

  12,930 
  

  

  15,080 
  

  

  7 
  

  

  Good. 
  

  

  1U00 
  

  

  14,190 
  

  

  8 
  

  

  Fair. 
  

  

  11,670 
  

  

  14,550 
  

  

  1 
  (Check-reading) 
  

  

  

  15,600 
  

  

  Mean 
  . 
  . 
  

  

  

  12,250 
  

  

  14,900 
  

  

  

  

  Figs. 
  2-9, 
  PL 
  II., 
  show 
  magnetization-curves 
  taken 
  on 
  the 
  

   ring 
  and 
  by 
  the 
  plug 
  on 
  the 
  mean 
  drilling 
  for 
  each 
  specimen. 
  

   It 
  will 
  be 
  noted 
  that 
  the 
  curve 
  obtained 
  by 
  the 
  plug 
  lies 
  below 
  

   that 
  for 
  the 
  ring 
  in 
  every 
  case 
  ; 
  but 
  there 
  is 
  no 
  evidence 
  to 
  

   show 
  that 
  this 
  is 
  due 
  to 
  an 
  air-gap. 
  If 
  such 
  a 
  gap 
  were 
  

   present, 
  of 
  approximately 
  equal 
  amount 
  in 
  each 
  of 
  the 
  

   specimens, 
  the 
  shearing-over 
  of 
  the 
  curves 
  of 
  the 
  wrought- 
  

   iron 
  and 
  mild-steel 
  specimens 
  would 
  be 
  much 
  more 
  marked 
  

   in 
  comparison 
  to 
  those 
  of 
  the 
  cast-iron 
  specimens, 
  owing 
  to 
  

   the 
  much 
  greater 
  permeability 
  and 
  induction-density 
  in 
  the 
  

   former. 
  

  

  Table 
  II. 
  is 
  obtained 
  from 
  the 
  curves 
  by 
  finding 
  the 
  value 
  

   of 
  IP, 
  the 
  nominal 
  magnetizing 
  force 
  in 
  the 
  case 
  of 
  the 
  plug- 
  

   test, 
  for 
  each 
  value* 
  of 
  H 
  from 
  the 
  ring-test, 
  for 
  a 
  given 
  

   induction-density; 
  and 
  fig. 
  10, 
  PL 
  II., 
  gives 
  curves 
  showing 
  

   the 
  relation 
  of 
  IP 
  to 
  H 
  for 
  each 
  of 
  the 
  materials 
  and 
  for 
  the 
  

   mean 
  of 
  all. 
  It 
  will 
  be 
  observed 
  that 
  although 
  there 
  are 
  

   considerable 
  differences 
  between 
  the 
  values 
  in 
  the 
  various 
  

   columns, 
  they 
  appear 
  to 
  have 
  no 
  relation 
  to 
  the 
  permeability 
  

   of 
  the 
  specimen, 
  and 
  must 
  therefore 
  be 
  regarded 
  as 
  acci- 
  

   dental. 
  In 
  fact, 
  the 
  difference 
  between 
  H 
  and 
  IP 
  is 
  greater 
  

   in 
  the 
  case 
  of 
  the 
  special 
  cast-iron 
  than 
  for 
  either 
  the 
  wrought- 
  

   iron 
  or 
  mild-steel 
  specimens, 
  which 
  is 
  exactly 
  contrary 
  to 
  the 
  

   effect 
  which 
  would 
  he 
  produced 
  by 
  an 
  air-gap. 
  The 
  difference 
  

   must 
  consequently 
  he 
  attributed 
  to 
  the 
  shortness 
  of 
  the 
  spe- 
  

   cimen 
  ; 
  and 
  the 
  results 
  therefore 
  may 
  have 
  some 
  general 
  value 
  

  

  in 
  indicating 
  the 
  amount 
  of 
  the 
  end 
  effect 
  in 
  the 
  case 
  of 
  voko- 
  

   permeameters, 
  in 
  which 
  the 
  specimen 
  i- 
  only 
  five 
  diameters 
  

   long. 
  

  

  