﻿444 
  Lord 
  Kelvin 
  on 
  a 
  New 
  Specifying 
  Method 
  for 
  

  

  The 
  4 
  cm. 
  spheres 
  seem 
  to 
  show 
  evidence, 
  at 
  the 
  distance 
  

   o£ 
  30 
  cms., 
  of 
  the 
  reversal 
  effect 
  mentioned 
  above, 
  but 
  it 
  

   disappeared 
  before 
  a 
  distance 
  of 
  50 
  cms. 
  was 
  reached. 
  With 
  

   the 
  other 
  spheres 
  no 
  trace 
  of 
  the 
  phenomenon 
  can 
  be 
  found, 
  

  

  No 
  difficulty 
  at 
  all 
  was 
  experienced 
  in 
  handling 
  the 
  smaller 
  

   spheres, 
  but 
  the 
  larger 
  ones 
  gave 
  some_irouble. 
  But 
  a 
  single 
  

   reading 
  had 
  been 
  secured 
  with 
  the 
  first 
  pair 
  of 
  10 
  cm. 
  shells 
  

   before 
  one 
  of 
  them 
  failed. 
  Veins 
  appeared 
  in 
  the 
  gold-leaf 
  

   encircling 
  one 
  platinum 
  cap. 
  On 
  replacing 
  this 
  sphere 
  by 
  a 
  

   new 
  one, 
  only 
  three 
  or 
  four 
  readings 
  were 
  secured 
  before 
  the 
  

   other 
  sphere 
  of 
  the 
  first 
  pair 
  failed 
  in 
  the 
  same 
  way. 
  This 
  

   was 
  removed 
  and 
  a 
  new 
  one 
  put 
  in 
  its 
  place, 
  and 
  with 
  the 
  

   pair 
  thus 
  formed 
  the 
  readings 
  in 
  Table 
  VII. 
  were 
  obtained. 
  

  

  If 
  curves 
  be 
  drawn 
  with 
  the 
  mean 
  readings 
  of 
  Tables 
  V., 
  

   VI., 
  and 
  VII. 
  as 
  ordinates 
  and 
  the^distances 
  from 
  the 
  oscillator 
  

   as 
  abscissae, 
  the 
  curve 
  for 
  a 
  shell 
  will 
  be 
  found 
  to 
  practicallv 
  

   coincide 
  with 
  that 
  for 
  the 
  solid 
  sphere 
  of 
  the 
  same 
  diameter. 
  

   The 
  experiments, 
  therefore, 
  indicate 
  that, 
  both 
  in 
  the 
  case 
  of 
  

   the 
  cylindrical 
  and 
  of 
  the 
  spherical 
  doublets, 
  the 
  excessivelv 
  

   thin 
  gold-leaf 
  shells 
  were 
  quite 
  as 
  efficient 
  as 
  the 
  solid 
  metal 
  

   bodies. 
  

  

  This 
  investigation 
  was 
  made 
  in 
  the 
  Jefferson 
  Physical 
  

   Laboratory, 
  Harvard 
  University 
  ; 
  and 
  while 
  under 
  especial 
  

   obligation 
  to 
  Professor 
  Trowbridge 
  for 
  his 
  never-failino- 
  

   consideration 
  and 
  encouragement, 
  I 
  would 
  express 
  my 
  grati- 
  

   tude 
  to 
  every 
  member 
  of 
  his 
  staff 
  for 
  innumerable 
  kindnesses. 
  

  

  Jefferson 
  Physical 
  Laboratory, 
  

   Harvard 
  University, 
  U.S. 
  

  

  XLIX. 
  A 
  Neid 
  Specifying 
  Method 
  for 
  Stress 
  and 
  Strain 
  in 
  

   an 
  Elastic 
  Solid. 
  By 
  Lord 
  Kelvin 
  *. 
  

  

  THE 
  method 
  for 
  specifying 
  stress 
  and 
  strain 
  hitherto 
  

   followed 
  by 
  all 
  writers 
  on 
  elasticity 
  has 
  the 
  great 
  

   disadvantage 
  that 
  it 
  essentially 
  requires 
  the 
  strain 
  to 
  be 
  

   infinitely 
  small. 
  As 
  a 
  notational 
  method 
  it 
  has 
  the 
  in- 
  

   convenience 
  that 
  the 
  specifying 
  elements 
  are 
  of 
  two 
  essentially 
  

   different 
  kinds 
  (in 
  the 
  notation 
  of 
  Thomson 
  and 
  Tait 
  e,f 
  g, 
  

   simple 
  elongations 
  ; 
  a, 
  b, 
  c, 
  shearings). 
  Both 
  these 
  faults 
  

   are 
  avoided 
  if 
  we 
  take 
  the 
  six 
  lengths 
  of 
  the 
  six 
  edges 
  of 
  a 
  

   tetrahedron 
  of 
  the 
  solid, 
  or, 
  what 
  amounts 
  to 
  the 
  same, 
  

   though 
  less 
  simple, 
  the 
  three 
  pairs 
  of 
  face-diagonals 
  of 
  a 
  

  

  * 
  Communicated 
  by 
  the 
  Author. 
  From 
  the 
  Proceedings 
  of 
  the 
  Eoval 
  

   Society 
  of 
  Edinburgh 
  of 
  Jan. 
  20, 
  of 
  which 
  a 
  preliminary 
  notice 
  was 
  

   published 
  in 
  the 
  Phil, 
  Mag. 
  for 
  Jan. 
  1902. 
  

  

  