﻿530 
  Mr. 
  W. 
  Williams 
  on 
  tlie 
  Temperature 
  Variation 
  of 
  

  

  is 
  seen 
  that 
  to 
  a 
  rough 
  approximation 
  — 
  = 
  ~. 
  The 
  deter- 
  

  

  X 
  <Ts 
  *" 
  s 
  

  

  mination 
  of 
  — 
  , 
  however, 
  is 
  a 
  matter 
  of 
  difficulty, 
  the 
  results 
  

  

  obtained 
  above 
  from 
  — 
  being 
  undoubtedly 
  imperfect 
  and 
  

   pe 
  

  

  unreliable. 
  Thus, 
  Omadei's 
  value 
  for 
  the 
  percentage 
  increase 
  

  

  of 
  volume 
  of 
  thallium 
  in 
  the 
  act 
  of 
  fusion 
  is 
  4*32, 
  whereas, 
  

  

  according 
  to 
  Toepler, 
  it 
  ought 
  to 
  be 
  3*22. 
  The 
  former 
  of 
  

  

  these 
  values 
  gives 
  X 
  e 
  =*081 
  and 
  — 
  = 
  1*84, 
  whereas 
  the 
  latter 
  

  

  X 
  s 
  

  

  gives 
  \ 
  e 
  = 
  -072, 
  and 
  r^= 
  1*64. 
  Moreover, 
  it 
  is 
  not 
  probable 
  

  

  A 
  i9 
  

  

  that 
  the 
  increase 
  of 
  resistance 
  that 
  accompanies 
  fusion 
  is 
  

   determined 
  by 
  the 
  increase 
  in 
  X 
  alone, 
  though 
  possibly 
  X 
  may 
  

   be 
  the 
  most 
  important 
  factor 
  concerned 
  in 
  the 
  matter. 
  At 
  

   any 
  rate 
  it 
  is 
  worthy 
  of 
  note 
  that, 
  whereas 
  in 
  the 
  case 
  of 
  

   metals 
  which 
  expand 
  on 
  melting 
  the 
  specific 
  resistance 
  is 
  

   greater 
  in 
  the 
  liquid 
  than 
  in 
  the 
  solid 
  state 
  at 
  the 
  temperature 
  

   of 
  fusion, 
  in 
  the 
  case 
  of 
  bismuth 
  and 
  antimony, 
  which 
  

   contract 
  on 
  melting, 
  it 
  is 
  less. 
  

  

  Platinum 
  and 
  palladium 
  differ 
  from 
  the 
  metals 
  already 
  

   discussed, 
  as 
  regards 
  their 
  temperature-coefficients, 
  in 
  the 
  

  

  fact 
  that 
  for 
  them 
  the 
  value 
  of 
  a 
  is 
  less 
  than 
  —=-„ 
  and 
  the 
  locus 
  

  

  "2 
  to 
  

  

  of 
  a 
  concave 
  towards 
  the 
  axis 
  of 
  temperature, 
  whereas, 
  in 
  the 
  

   case 
  of 
  the 
  other 
  and 
  apparently 
  simpler 
  metals, 
  a 
  is 
  greater 
  

  

  than 
  ^=-x 
  and 
  the 
  locus 
  of 
  a 
  convex 
  towards 
  that 
  axis. 
  This 
  

  

  anomaly 
  indicates 
  that 
  for 
  platinum 
  and 
  palladium, 
  the 
  

   temperature-variation 
  o£ 
  the 
  electronization-coefficient 
  q 
  

   cannot 
  be 
  accounted 
  for 
  by 
  the 
  temperature-variations 
  of 
  X 
  

   and 
  \ 
  as 
  in 
  the 
  case 
  of 
  the 
  simpler 
  metals. 
  Some 
  other 
  

   factor 
  has 
  to 
  be 
  superposed 
  upon 
  these 
  in 
  order 
  to 
  convert 
  

   into 
  an 
  increase 
  the 
  decrease 
  that 
  would 
  arise 
  in 
  q 
  from 
  them 
  

   alone. 
  The 
  thermoelectric 
  curves 
  of 
  platinum 
  and 
  palladium 
  

   are 
  also 
  exceptional 
  as 
  compared 
  to 
  those 
  of 
  the 
  simpler 
  

   metals. 
  For 
  whereas 
  the 
  curves, 
  as 
  given 
  by 
  Fleming 
  and 
  

   Dewar, 
  have 
  a 
  positive 
  curvature 
  for 
  the 
  simpler 
  metals, 
  for 
  

   platinum 
  and 
  palladium 
  the 
  curvature 
  is 
  decidedly 
  negative. 
  

   These 
  exceptional 
  characteristics 
  are 
  probably 
  closely 
  related, 
  

   since 
  on 
  the 
  electronic 
  theory 
  both 
  the 
  electrical 
  resistance 
  

   and 
  the 
  thermoelectric 
  properties 
  of 
  a 
  metal 
  depend 
  upon 
  the 
  

   electronization-coefficient 
  q. 
  

  

  As 
  might 
  be 
  expected 
  from 
  their 
  ferro-magnetic 
  properties, 
  

  

  