﻿516 
  Mr. 
  W. 
  Williams 
  on 
  the 
  Temperature 
  Variation 
  oj 
  

  

  The 
  resistance 
  of 
  a 
  metal 
  is 
  approximately 
  proportional 
  to 
  

  

  the 
  absolute 
  temperature. 
  Hence 
  a 
  = 
  — 
  — 
  • 
  , 
  where 
  6 
  is 
  

  

  the 
  absolute 
  temperature, 
  so 
  that 
  the 
  specific 
  resistance 
  in 
  the 
  

  

  solid 
  state 
  at 
  the 
  temperature 
  of 
  fusion 
  is 
  — 
  - 
  — 
  . 
  Now, 
  the 
  

   1 
  273 
  

  

  resistance 
  of 
  pure 
  mercury 
  in 
  the 
  solid 
  state 
  has 
  been 
  very 
  

  

  carefully 
  investigated 
  by 
  Dr. 
  Fleming 
  (Proc. 
  Royal 
  Society, 
  

  

  vol. 
  Ix. 
  No. 
  359, 
  p. 
  79). 
  According 
  to 
  his 
  results, 
  the 
  

  

  process 
  of 
  fusion 
  appears 
  to 
  set 
  in 
  at 
  — 
  50° 
  C, 
  and 
  is 
  not 
  

  

  properly 
  completed 
  until 
  — 
  36° 
  C. 
  is 
  reached, 
  the 
  value 
  of 
  

  

  a 
  at 
  — 
  50° 
  C. 
  just 
  before 
  fusion 
  begins 
  being 
  21. 
  By 
  

  

  calculation, 
  taking 
  m 
  to 
  be 
  2, 
  and 
  V 
  = 
  14*l, 
  we 
  get 
  17*8. 
  

  

  Again, 
  at 
  —95° 
  C. 
  ( 
  — 
  100° 
  C. 
  on 
  the 
  pt 
  scale), 
  the 
  calculated 
  

  

  value 
  is 
  14'4, 
  Dr. 
  Fleming's 
  value 
  being 
  15*5. 
  

  

  The 
  melting-point 
  of 
  calcium 
  is 
  not 
  definitely 
  given. 
  The 
  

   metal, 
  however, 
  is 
  said 
  to 
  melt 
  at 
  i( 
  red 
  heat," 
  and 
  will 
  

   therefore 
  have 
  a 
  melting-point 
  between 
  500° 
  C. 
  and 
  600° 
  C, 
  

   so 
  that 
  T 
  is 
  about 
  853. 
  Hence, 
  m 
  being 
  2 
  and 
  V 
  25'4, 
  

   o- 
  = 
  10'6, 
  Matthiessen's 
  value 
  being 
  7'5*. 
  

  

  Taken 
  as 
  a 
  whole, 
  the 
  accordance 
  between 
  cr 
  and 
  a' 
  is 
  not 
  

   unsatisfactory, 
  being 
  about 
  the 
  same 
  as 
  the 
  accordance 
  

   observed 
  in 
  the 
  case 
  of 
  the 
  law 
  of 
  Dulong 
  and 
  Petit 
  as 
  to 
  

   atomic 
  heat, 
  Thus, 
  taking 
  6'3 
  for 
  the 
  constant 
  of 
  that 
  law, 
  

   the 
  value 
  is 
  15 
  per 
  cent, 
  above 
  it 
  in 
  the 
  case 
  of 
  calcium, 
  and 
  

   20 
  per 
  cent, 
  below 
  it 
  in 
  the 
  case 
  of 
  sulphur. 
  Also, 
  con- 
  

   sidering 
  the 
  wide 
  variations 
  that 
  occur 
  in 
  the 
  values 
  of 
  m, 
  V, 
  

   T, 
  and 
  cr, 
  the 
  accordance 
  cannot 
  be 
  regarded 
  as 
  a 
  matter 
  of 
  

   accident, 
  but 
  must 
  be 
  taken 
  as 
  an 
  indication 
  of 
  a 
  definite 
  

   physical 
  law. 
  

  

  Certain 
  metals, 
  however, 
  fail 
  to 
  conform 
  with 
  the 
  relation 
  

   for 
  cr 
  although 
  they 
  are 
  closely 
  related, 
  both 
  physically 
  and 
  

   chemically, 
  to 
  those 
  that 
  do. 
  Thus 
  gold, 
  indium, 
  tin, 
  and 
  

   aluminium 
  fail, 
  although 
  the 
  first 
  is 
  allied 
  to 
  copper 
  and 
  

   silver, 
  the 
  second 
  to 
  thallium, 
  and 
  the 
  third 
  to 
  lead. 
  Thus: 
  — 
  

  

  Gold 
  

  

  Indium 
  

  

  Tin 
  

  

  Aluminium 
  

  

  ! 
  - 
  

  

  i 
  

  

  V. 
  

  

  T. 
  

  

  <r. 
  

  

  a'. 
  

  

  i 
  

  

  10-1 
  

  

  1310 
  

  

  3-99 
  

  

  2-0 
  

  

  3 
  

  

  15"3 
  

  

  440 
  

  

  17-64 
  

  

  8-4 
  

  

  4 
  

  

  16-3 
  

  

  503 
  

  

  22-05 
  

  

  10-5 
  

  

  ! 
  » 
  

  

  106 
  

  

  923 
  

  

  5-94 
  

  

  2-9 
  

  

  * 
  The 
  melting-point 
  of 
  calcium 
  is 
  probably 
  underestimated, 
  800° 
  C, 
  

   or 
  1073 
  absolute 
  being 
  perhaps 
  more 
  nearly 
  correct. 
  

  

  