﻿392 
  

  

  Richards 
  and 
  Trowbridge 
  — 
  Conductivity, 
  etc. 
  

  

  heat 
  of 
  the 
  material 
  which 
  must 
  be 
  warmed 
  in 
  the 
  latter 
  case. 
  

   The 
  average 
  temperature 
  of 
  the 
  solution 
  rose 
  during 
  our 
  experi- 
  

   ments 
  only 
  at 
  a 
  rate 
  of 
  about 
  1° 
  in 
  three 
  minutes. 
  

  

  

  2 
  4 
  6 
  8 
  10 
  12 
  14 
  

  

  Ohms 
  are 
  plotted 
  horizontally. 
  Half 
  oscillations 
  are 
  plotted 
  vertically. 
  

  

  A 
  similar, 
  although 
  smaller, 
  heat 
  capacity 
  prevents 
  the 
  wire 
  

   resistances 
  which 
  are 
  used 
  as 
  standards 
  from 
  becoming 
  seriously 
  

   altered 
  in 
  resistance 
  by 
  the 
  heat. 
  We 
  had 
  used 
  manganin 
  wire 
  

   in 
  our 
  tests, 
  but 
  in 
  order 
  to 
  be 
  sure 
  that 
  our 
  fine 
  short 
  wires 
  

   had 
  not 
  been 
  overheated, 
  we 
  constructed 
  a 
  five-ohm 
  resistance 
  

   of 
  four 
  strands 
  of 
  coarser 
  manganin 
  wire 
  about 
  0'25 
  mm 
  diameter 
  

   and 
  3'5 
  meters 
  long. 
  This 
  was 
  stretched 
  upon 
  each 
  side 
  of 
  a 
  

   thin 
  vulcanite 
  plate 
  to 
  avoid 
  self-induction, 
  but 
  it 
  allowed 
  essen- 
  

   tially 
  the 
  same 
  number 
  of 
  oscillations 
  to 
  pass 
  as 
  did 
  the 
  short 
  

   fine 
  wire. 
  A 
  short 
  German-silver 
  wire, 
  with 
  a 
  \ery 
  high 
  tem- 
  

   perature-coefficient, 
  showed 
  a 
  conductivity 
  only 
  a 
  very 
  little 
  

  

  