﻿228 
  

  

  Mr. 
  R. 
  Mallet 
  on 
  the 
  alleged 
  Expansion 
  

  

  paper, 
  and 
  assuming 
  the 
  depth 
  of 
  the 
  colder 
  of 
  these 
  columns, 
  whether 
  

   that 
  be 
  at 
  the 
  circumference 
  or 
  not, 
  to 
  be, 
  as 
  stated, 
  36", 
  that 
  of 
  the 
  hotter 
  

   column 
  will 
  be 
  36*0000005514, 
  and 
  the 
  difference 
  between 
  these 
  two 
  

   measures 
  the 
  force 
  which 
  alone 
  can 
  produce 
  circulating 
  currents 
  in 
  the 
  

   mass 
  by 
  differences 
  of 
  temperature 
  due 
  only 
  to 
  cooling. 
  This 
  is 
  equally 
  

   true 
  whether 
  it 
  be 
  the 
  colder 
  column 
  that 
  is 
  dilated, 
  as 
  supposed 
  by 
  

   Messrs. 
  Nasmyth 
  and 
  Carpenter, 
  or 
  the 
  hotter 
  one, 
  as 
  is 
  the 
  fact. 
  And 
  

   if 
  we 
  consider 
  the 
  viscidity 
  of 
  molten 
  cast 
  iron, 
  it 
  is 
  perfectly 
  obvious 
  

   that 
  the 
  circulating 
  currents 
  referred 
  to 
  by 
  Messrs. 
  Nasmyth 
  and 
  Car- 
  

   penter 
  cannot 
  be 
  due 
  to 
  so 
  insignificant 
  a 
  cause. 
  

  

  Want 
  of 
  attention, 
  or 
  careless 
  interpretation 
  of 
  the 
  many 
  and 
  some- 
  

   what 
  complicated 
  conditions 
  thus 
  seen 
  to 
  be 
  involved 
  in 
  the 
  cooling 
  of 
  a 
  

   solid 
  by 
  dissipation 
  of 
  its 
  heat 
  from 
  its 
  exterior, 
  has 
  caused 
  many 
  seri- 
  

   ous 
  misapprehensions 
  on 
  the 
  part 
  of 
  experimenters 
  as 
  to 
  the 
  supposed 
  

   expansion 
  of 
  metals 
  in 
  volume 
  when 
  consolidating. 
  Thus, 
  even 
  in 
  the 
  

   case 
  of 
  bismuth, 
  it 
  has 
  been 
  supposed 
  a 
  conclusive 
  proof 
  of 
  its 
  expan- 
  

   sion 
  that 
  a 
  mass 
  cooling 
  in 
  an 
  open 
  crucible 
  exudes 
  from 
  its 
  interior 
  

   upon 
  its 
  top 
  surface 
  cauliflower-like 
  excrescences 
  ; 
  but 
  although 
  the 
  author 
  

   does 
  not 
  here 
  deny 
  or 
  affirm 
  any 
  thing 
  as 
  to 
  expansion 
  being 
  a 
  fact 
  in 
  the 
  

   case 
  of 
  bismuth, 
  it 
  is 
  nevertheless 
  obvious 
  that 
  such 
  excrescences 
  might 
  

   arise 
  merely 
  from 
  the 
  grip 
  of 
  the 
  crucible 
  itself, 
  or 
  even 
  of 
  the 
  exterior 
  

   portions 
  of 
  the 
  metal 
  already 
  solidified 
  contracting 
  upon 
  and 
  so 
  squeez- 
  

   ing 
  out 
  portions 
  of 
  the 
  still 
  liquid 
  interior. 
  

  

  It 
  is 
  stated 
  on 
  good 
  authority 
  that 
  a 
  distinguished 
  artillery 
  officer, 
  in 
  

   former 
  years 
  at 
  the 
  head 
  of 
  the 
  Laboratory, 
  Woolwich 
  Arsenal, 
  satisfied 
  

   himself 
  of 
  the 
  reality 
  of 
  the 
  expansion 
  

   of 
  cast 
  iron 
  in 
  consolidating 
  by 
  the 
  Tig. 
  8. 
  

  

  following 
  experiment 
  : 
  — 
  An 
  elon- 
  

   gated 
  projectile 
  was 
  cast, 
  with 
  its 
  axis 
  

   vertical, 
  in 
  a 
  very 
  thick 
  and 
  massive 
  

   mould 
  of 
  cast 
  iron, 
  the 
  mould 
  being 
  

   cold 
  or 
  nearly 
  so 
  ; 
  the 
  molten 
  metal 
  

   was 
  introduced 
  through 
  a 
  narrow 
  

   aperture 
  applied 
  at 
  the 
  base 
  of 
  the 
  

   projectile, 
  as 
  in 
  fig. 
  8, 
  the 
  neck 
  or 
  

   " 
  gate 
  " 
  being 
  knocked 
  off 
  the 
  in- 
  

   stant 
  the 
  mould 
  was 
  filled. 
  As 
  the 
  

   cooling 
  rapidly 
  proceeded, 
  portions 
  

   of 
  the 
  still 
  fluid 
  metal 
  were 
  forced 
  

   out 
  at 
  the 
  place 
  where 
  this 
  neck 
  

   was 
  detached; 
  and 
  the 
  conclusion 
  was 
  

   come 
  to 
  that 
  the 
  exterior 
  being 
  al- 
  

   ready 
  solidified 
  such 
  excrescence 
  could 
  

   only 
  arise 
  from 
  expansion 
  of 
  the 
  contained 
  liquid 
  metal 
  as 
  it 
  solidified 
  

   in 
  succession. 
  What 
  really 
  did 
  take 
  place, 
  and 
  is 
  the 
  true 
  explanation 
  

  

  