﻿12 
  G. 
  V. 
  Maclean 
  — 
  Velocity 
  of 
  Electric 
  Waves 
  in 
  Air. 
  

  

  The 
  velocity 
  of 
  the 
  electric 
  waves 
  was 
  determined 
  from 
  the 
  

   formula 
  X 
  = 
  yT 
  = 
  '^nY^hC 
  where 
  X 
  is 
  the 
  wave-length, 
  L 
  the 
  

   self-induction, 
  C 
  the 
  capacity, 
  V 
  the 
  velocity 
  and 
  T 
  the 
  time 
  

   of 
  oscillation 
  of 
  the 
  secondary 
  spark. 
  T 
  was 
  found 
  by 
  

   the 
  photographic 
  process. 
  The 
  sparks 
  directly 
  given 
  by 
  

   the 
  oscillator 
  used 
  in 
  the 
  original 
  experiment 
  could 
  not 
  

   be 
  photographed. 
  They 
  were 
  too 
  small 
  and, 
  moreover, 
  

   their 
  light 
  was 
  not 
  actinic 
  enough. 
  Sparks 
  given 
  by 
  similar 
  

   capacity 
  and 
  self-induction 
  but 
  of 
  larger 
  dimensions 
  and 
  cad- 
  

   mium 
  points 
  in 
  place 
  of 
  the 
  platinum 
  globules 
  were 
  photo- 
  

   graphed. 
  The 
  self-induction 
  here 
  used 
  consisted 
  of 
  two 
  parallel 
  

  

  copper 
  wires 
  of 
  the 
  same 
  diameter 
  as 
  were 
  employed 
  in 
  the 
  

   original 
  experiment, 
  5 
  cm. 
  apart 
  and 
  1051'1 
  cm. 
  in 
  length. 
  

   The 
  capacity 
  was 
  the 
  same 
  glass 
  plate 
  with 
  the 
  tin 
  foil 
  sheets 
  

   four 
  times 
  as 
  large. 
  The 
  time 
  of 
  oscillation 
  of 
  the 
  sparks 
  thus 
  

   produced 
  was 
  found 
  to 
  be 
  4-12382 
  X 
  10" 
  "^ 
  = 
  T' 
  seconds. 
  It 
  

   was 
  then 
  assumed, 
  that 
  the 
  formula 
  must 
  still 
  hold 
  good 
  if 
  we 
  

   cut 
  down 
  the 
  self-induction 
  and 
  capacity, 
  still 
  keeping 
  the 
  

   copper 
  wires 
  5 
  cm. 
  apart. 
  That 
  is 
  to 
  say, 
  if 
  we 
  make 
  our 
  C 
  one- 
  

   fourth 
  and 
  our 
  L 
  y 
  J 
  o*^^ 
  ^^ 
  ^^^® 
  ^ 
  ^^^^^ 
  ^" 
  ^^^^ 
  photographic 
  

   process 
  the 
  time 
  of 
  oscillation 
  of 
  our 
  spark 
  will 
  be 
  -g-^^th 
  of 
  

   that 
  of 
  the 
  spark 
  photographed. 
  In 
  the 
  original 
  experiment 
  

   the 
  area 
  of 
  the 
  tin 
  foil 
  was 
  just 
  one-fourth 
  of 
  that 
  on 
  the 
  con- 
  

   denser 
  which 
  formed 
  the 
  capacity 
  for 
  the 
  spark 
  photographed, 
  

  

  whereas 
  the 
  length 
  of 
  copper 
  wire 
  was 
  9*02 
  cms, 
  being- 
  ;:r 
  

  

  of 
  what 
  was 
  used 
  in 
  the 
  photographic 
  process. 
  Accordingly 
  

  

  