﻿260 
  Pierce 
  — 
  Measurement 
  of 
  Short 
  Electric 
  Waves. 
  

  

  The 
  transparency 
  of 
  this 
  board 
  with 
  the 
  grain 
  parallel 
  to 
  the 
  

   electric 
  oscillation 
  is 
  about 
  60 
  per 
  cent 
  of 
  its 
  transparency 
  with 
  

   the 
  grain 
  perpendicular. 
  Another 
  set 
  of 
  measurements 
  gave 
  

   for 
  this 
  quantity 
  the 
  value 
  59*2. 
  For 
  these 
  two 
  orientations, 
  

   white 
  oak 
  and 
  white 
  wood 
  show 
  very 
  small 
  differences 
  respec- 
  

   tively 
  in 
  their 
  transparencies. 
  The 
  striking 
  characteristic 
  of 
  

   pine 
  in 
  this 
  respect 
  is 
  undoubtedly 
  due 
  to 
  difference 
  between 
  

   its 
  electric 
  conductivity 
  in 
  and 
  across 
  the 
  grain. 
  

  

  A 
  grating 
  formed 
  of 
  strips 
  of 
  metal 
  2 
  cm 
  wide 
  and 
  2 
  cm 
  apart 
  

   was 
  found 
  to 
  transmit 
  96^ 
  of 
  the 
  incident 
  waves 
  when 
  the 
  

   strips 
  were 
  across 
  the 
  oscillator, 
  and 
  29^ 
  when 
  the 
  strips 
  were 
  

   parallel 
  thereto. 
  

  

  A 
  single 
  rod 
  of 
  brass 
  3/16 
  inch 
  in 
  diameter, 
  placed 
  between 
  

   the 
  oscillator 
  and 
  the 
  resonator 
  parallel 
  to 
  the 
  electric 
  displace- 
  

   ment, 
  was 
  found 
  to 
  screen 
  off 
  40^ 
  of 
  the 
  waves. 
  

  

  These 
  simple 
  experiments 
  are 
  intended 
  merely 
  to 
  show 
  the 
  

   adaptability 
  of 
  the 
  apparatus 
  to 
  quantitative 
  work 
  with 
  electric 
  

   waves. 
  Other 
  investigations 
  are 
  in 
  progress. 
  

  

  Jefferson 
  Physical 
  Laboratory, 
  

   Harvard 
  University. 
  

  

  