﻿Prof. 
  J. 
  Trowbridge 
  on 
  the 
  Induction 
  Coil. 
  393 
  

  

  of 
  a 
  short 
  tube 
  or 
  the 
  fourth 
  of 
  a 
  longer 
  one, 
  &c, 
  &c. 
  This 
  

   is 
  contrary 
  to 
  what 
  is 
  implied 
  by 
  some 
  writers. 
  

  

  6. 
  The 
  pressures 
  for 
  identical 
  notes 
  on 
  trumpet 
  and 
  cornet 
  

   are 
  almost 
  the 
  same 
  for 
  any 
  given 
  intensity, 
  but 
  very 
  much 
  

   less 
  than 
  those 
  for 
  the 
  same 
  notes 
  on 
  the 
  trombone. 
  See 
  

   Table 
  VI. 
  and 
  Plate 
  VIII. 
  (cf. 
  with 
  Table 
  III. 
  and 
  Plate 
  VII.) 
  . 
  

  

  7. 
  The 
  pressures 
  used 
  for 
  loud 
  low 
  notes 
  may 
  exceed 
  those 
  

   for 
  soft 
  high 
  notes, 
  in 
  some 
  cases 
  even 
  where 
  the 
  notes 
  are 
  an 
  

   octave 
  apart. 
  See 
  Tables 
  III., 
  IV., 
  V., 
  and 
  VI., 
  also 
  Pis. 
  VII. 
  

   & 
  VIII. 
  

  

  8. 
  The 
  present 
  results 
  as 
  to 
  maximum 
  and 
  minimum 
  pres- 
  

   sures 
  are 
  in 
  accord 
  with 
  Dr. 
  Stone's, 
  so 
  far 
  as 
  comparison 
  is 
  

   possible. 
  

  

  Our 
  thanks 
  are 
  due 
  to 
  Mr. 
  Pickerill 
  for 
  kindly 
  placing 
  his 
  

   services 
  at 
  our 
  disposal. 
  

  

  University 
  College, 
  Nottingham, 
  

   August 
  1901. 
  

  

  XLIII. 
  The 
  Induction 
  Coil. 
  By 
  Prof. 
  John 
  Trowbridge 
  *. 
  

  

  LORD 
  Rayleigh, 
  in 
  a 
  recent 
  article 
  (Philosophical 
  

   Magazine, 
  Dec. 
  1901), 
  has 
  shown 
  the 
  significance 
  of 
  

   the 
  electrostatic 
  capacity 
  between 
  the 
  primary 
  and 
  the 
  

   secondary 
  of 
  the 
  induction-coil, 
  and 
  has 
  proved 
  that 
  in 
  certain 
  

   cases 
  a 
  condenser 
  in 
  the 
  primary 
  is 
  of 
  no 
  advantage, 
  and 
  in 
  

   certain 
  cases 
  maybe 
  prejudicial. 
  

  

  The 
  performance 
  of 
  a 
  powerful 
  coil 
  devised 
  by 
  Mr. 
  Heinze, 
  

   of 
  Boston, 
  U.S., 
  for 
  me, 
  operated 
  by 
  his 
  liquid 
  interrupter, 
  

   justifies 
  the 
  points 
  raised 
  by 
  Lord 
  Rayleigh 
  ; 
  and, 
  on 
  account 
  

   of 
  the 
  importance 
  of 
  the 
  induction-coil 
  in 
  wireless 
  telegraphy, 
  

   merits 
  I 
  think 
  wider 
  knowledge 
  than 
  it 
  has 
  received. 
  

  

  The 
  dimensions 
  of 
  the 
  coil 
  are 
  as 
  follows 
  : 
  — 
  

  

  Length 
  of 
  iron 
  of 
  primary 
  coil, 
  48 
  inches. 
  

   Diameter 
  of 
  „ 
  „ 
  ,, 
  3J 
  ,, 
  

  

  Wound 
  with 
  one 
  layer 
  of 
  no. 
  6 
  copper 
  wire. 
  

  

  The 
  secondary 
  coil 
  consists 
  of 
  140 
  coils 
  separated 
  from 
  

   each 
  other 
  by 
  plates 
  of 
  glass 
  one 
  eighth 
  of 
  an 
  inch 
  thick. 
  

   Each 
  of 
  these 
  coils 
  is 
  wound 
  with, 
  between 
  400 
  and 
  500 
  turns, 
  

   fine 
  wire. 
  The 
  entire 
  resistance 
  of 
  the 
  secondary 
  coil 
  is 
  

   246,600 
  ohms. 
  

  

  The 
  secondary 
  is 
  merely 
  inclosed 
  in 
  a 
  box. 
  By 
  unscrewing 
  

   the 
  cover 
  of 
  this 
  box 
  the 
  sectional 
  coils 
  can 
  be 
  inspected, 
  and 
  

   any 
  sectional 
  coil 
  can 
  be 
  removed 
  if 
  its 
  insulation 
  breaks 
  

   down 
  ; 
  for 
  the 
  coils 
  are 
  not 
  imbedded 
  in 
  paraffin. 
  It 
  was 
  

  

  * 
  Communicated 
  by 
  the 
  Author. 
  

   Phil. 
  Mag. 
  S. 
  6. 
  Vol 
  3. 
  No. 
  16. 
  April 
  1902, 
  2 
  D 
  

  

  