﻿Volta 
  Electricity 
  of 
  Metals. 
  425 
  

  

  § 
  68. 
  One 
  of 
  the 
  copper 
  plates 
  used 
  was 
  hollow 
  and 
  could 
  

   be 
  filled 
  with 
  water 
  and 
  a 
  thermometer 
  inserted, 
  but 
  with 
  the 
  

   other 
  plates 
  other 
  methods 
  of 
  measuring 
  temperature 
  had 
  to 
  

   be 
  adopted. 
  In 
  some 
  cases 
  the 
  temperature 
  was 
  measured 
  

   thermo-electrically, 
  while 
  in 
  others 
  a 
  simpler 
  and 
  more 
  rapid 
  

   mode 
  of 
  measurement 
  was 
  used, 
  which, 
  though 
  not 
  very 
  

   accurate, 
  is 
  quite 
  reliable 
  within 
  certain 
  limits. 
  

  

  § 
  69. 
  By 
  touching 
  the 
  back 
  of 
  the 
  plate 
  I 
  found 
  that 
  its 
  

   temperature 
  could 
  be 
  judged 
  as 
  " 
  tepid, 
  " 
  " 
  slightly 
  warm," 
  

   "warm/' 
  "very 
  warm/' 
  and 
  so 
  on. 
  It 
  was 
  found 
  experi- 
  

   mentally 
  that 
  these 
  terms 
  correspond 
  to 
  constant 
  temperatures 
  ; 
  

   or 
  rather 
  that 
  each 
  term 
  denotes 
  a 
  small 
  range 
  of 
  temperature, 
  

   the 
  middle 
  point 
  of 
  which 
  may 
  be 
  taken 
  as 
  corresponding 
  to 
  

   the 
  term. 
  In 
  determining 
  the 
  values 
  of 
  these 
  terms 
  a 
  plate 
  

   was 
  used 
  in 
  which 
  a 
  thermometer 
  was 
  inserted. 
  One 
  observer 
  

   touched 
  the 
  plate 
  with 
  the 
  tips 
  of 
  the 
  first 
  and 
  second 
  fingers 
  

   and 
  judged 
  its 
  state, 
  naming 
  it 
  by 
  one 
  of 
  the 
  terms, 
  "warm," 
  

   " 
  tepid," 
  &c, 
  the 
  other 
  observed 
  the 
  thermometer, 
  and 
  the 
  

   temperatures 
  found 
  to 
  correspond 
  to 
  each 
  term 
  are 
  as 
  

   follows 
  : 
  — 
  

  

  Cold 
  16° 
  C. 
  

  

  Quite 
  cool 
  24 
  

  

  Cool 
  28 
  

  

  Rather 
  cool 
  30 
  

  

  Tepid 
  , 
  35 
  

  

  Slightly 
  warm 
  40 
  

  

  Warm 
  47 
  

  

  Verv 
  warm 
  50 
  

  

  Hot 
  53 
  

  

  Very 
  hot 
  57 
  

  

  Too 
  hot 
  to 
  touch 
  continuously 
  63 
  

  

  Too 
  hot 
  to 
  touch 
  for 
  more 
  than 
  one 
  second 
  . 
  . 
  73 
  

  

  This 
  method 
  of 
  measuring 
  temperature 
  is 
  rough 
  and 
  ready, 
  

   but 
  since 
  the 
  possible 
  errors 
  are 
  within 
  limits 
  of 
  a 
  very 
  

   few 
  degrees, 
  one 
  only 
  requires 
  to 
  take 
  the 
  average 
  of 
  a 
  

   considerable 
  number 
  of 
  results 
  in 
  order 
  to 
  arrive 
  at 
  a 
  very 
  

   fair 
  approximation 
  to 
  the 
  true 
  values. 
  In 
  experiments 
  on 
  

   contact 
  electricity 
  in 
  air 
  there 
  are 
  so 
  many 
  possible 
  causes 
  of 
  

   disturbance 
  that 
  extremely 
  accurate 
  measurement 
  of 
  the 
  

   temperature 
  is 
  of 
  little 
  use, 
  especially 
  if 
  it 
  require 
  that 
  much 
  

   time 
  be 
  spent 
  over 
  each 
  reading. 
  

  

  § 
  70. 
  As 
  a 
  rule 
  the 
  upper 
  plate 
  was 
  heated, 
  in 
  order 
  that 
  

   the 
  lower 
  plate 
  might 
  not 
  be 
  affected 
  by 
  draughts 
  of 
  hot 
  air, 
  

   as 
  would 
  have 
  been 
  the 
  case 
  if 
  the 
  lower 
  had 
  been 
  hot 
  and 
  

   the 
  upper 
  cold. 
  Sometimes, 
  during 
  the 
  time 
  of 
  cooling, 
  the 
  

   upper 
  part 
  of 
  the 
  apparatus, 
  including 
  of 
  course 
  the 
  upper 
  

  

  