﻿454 
  H. 
  D. 
  Day 
  — 
  Magnetic 
  Increment 
  

  

  Constants 
  of 
  helix. 
  

  

  Length, 
  249 
  m 
  . 
  

  

  Gauge 
  of 
  wire, 
  80 
  turns 
  = 
  7'5 
  cm 
  . 
  

  

  Outside 
  circumferences 
  of 
  layers 
  of 
  helix 
  : 
  — 
  

  

  1st 
  layer 
  -0470 
  m 
  

  

  2d 
  " 
  -0518 
  

  

  3d 
  " 
  _.. 
  -0569 
  

  

  4th 
  " 
  _._ 
  -0620 
  

  

  5th 
  " 
  -0667 
  

  

  6th 
  " 
  -0722 
  

  

  7th 
  " 
  -6767 
  

  

  8th 
  " 
  -0827 
  

  

  Formula 
  for 
  strength 
  of 
  field. 
  

   Mean 
  field 
  (in 
  dynes) 
  along 
  the 
  axis 
  within 
  the 
  helix 
  : 
  — 
  

  

  where 
  &=distance 
  of 
  any 
  point 
  on 
  axis 
  of 
  coil 
  from 
  center 
  of 
  coil. 
  

   r=radius 
  of 
  coil. 
  

   2a= 
  length 
  of 
  coil. 
  

   n=total 
  number 
  of 
  turns 
  in 
  coil. 
  

   I=intensity 
  of 
  current 
  in 
  C. 
  G. 
  S. 
  units. 
  

  

  From 
  these 
  constants, 
  it 
  is 
  seen 
  that 
  the 
  iron 
  wire 
  within 
  

   the 
  helix 
  was 
  exposed 
  throughout 
  its 
  length 
  to 
  the 
  magnetizing 
  

   influence 
  of 
  fields 
  whose 
  mean 
  strength 
  along 
  the 
  axis 
  of 
  the 
  

   helix 
  reached 
  the 
  maximum 
  value 
  of 
  1,600 
  C. 
  G. 
  S. 
  units. 
  

  

  Daring 
  the 
  course 
  of 
  the 
  experiments, 
  fresh 
  sets 
  of 
  wires 
  

   varying 
  in 
  diameter 
  from 
  -48 
  mm 
  to 
  -18 
  mm 
  were 
  frequently 
  

   inserted 
  in 
  the 
  apparatus, 
  and 
  the 
  examination 
  of 
  the 
  incre- 
  

   ment 
  of 
  rigidity 
  was 
  carried 
  out 
  in 
  full 
  for 
  each 
  set. 
  Different 
  

   amounts 
  of 
  twist 
  were 
  locked 
  up 
  in 
  the 
  countertwisted 
  wires 
  

   and 
  at 
  definite 
  stages 
  in 
  the 
  twisting 
  process 
  the 
  upper 
  wire 
  

   was 
  exposed 
  to 
  the 
  magnetic 
  field 
  of 
  the 
  surrounding 
  helix, 
  

   which 
  was 
  varied 
  in 
  strength 
  by 
  successive 
  increments 
  of 
  25, 
  

   50, 
  or 
  100 
  units 
  from 
  zero 
  to 
  the 
  maximum 
  value 
  given 
  above. 
  

   For 
  each 
  definite 
  value 
  of 
  the 
  field-strength, 
  the 
  initial 
  twist, 
  0, 
  

   was 
  noted 
  and 
  the 
  corresponding 
  increment 
  of 
  rigidity 
  regis- 
  

   tered 
  as 
  a 
  scale-deflection. 
  

  

  Marked 
  effects 
  of 
  viscosity 
  were 
  in 
  evidence 
  throughout 
  the 
  

   experiments, 
  and 
  hysteresis 
  w 
  r 
  as 
  frequently 
  observed. 
  The 
  

   method 
  furnished 
  an 
  excellent 
  means 
  for 
  observing 
  the 
  latter. 
  

   The 
  effects 
  of 
  viscosity 
  were, 
  however, 
  irregular 
  in 
  all 
  ways. 
  

   They 
  were 
  most 
  pronounced 
  as 
  the 
  elastic 
  limit 
  of 
  the 
  wires 
  

   was 
  approached,- 
  — 
  roughly, 
  when 
  6 
  equalled 
  47r. 
  Viscous 
  slip 
  

   was 
  indicated, 
  sometimes 
  by 
  progressive, 
  sometimes 
  by 
  jerky, 
  

   scale-deflections, 
  according 
  as 
  the 
  cohesion 
  of 
  a 
  few 
  molecules 
  

  

  