﻿508 
  

  

  Prof. 
  O. 
  Reynolds 
  on 
  Rolling 
  -Friction. 
  [June 
  17, 
  

  

  explanation. 
  When 
  the 
  roller 
  rests 
  on 
  a 
  horizontal 
  surface 
  and 
  is 
  very 
  

   slightly 
  disturbed, 
  it 
  does 
  not 
  move 
  off, 
  but 
  oscillates 
  backwards 
  and 
  for- 
  

   wards. 
  This 
  happens 
  on 
  all 
  kinds 
  of 
  elastic 
  surfaces 
  ; 
  on 
  soft 
  india- 
  

   rubber 
  the 
  oscillations 
  are 
  both 
  large 
  and 
  continue 
  for 
  some 
  time. 
  Now 
  

   if 
  the 
  deformation 
  in 
  the 
  surface 
  of 
  the 
  rubber 
  were 
  complete, 
  there 
  would 
  

   be 
  no 
  tendency 
  to 
  bring 
  the 
  roller 
  back 
  ; 
  but 
  since, 
  owing 
  to 
  friction, 
  the 
  

   india-rubber, 
  under 
  the 
  advancing 
  side 
  of 
  the 
  roller, 
  is 
  prevented 
  from 
  

   extending 
  while 
  that 
  under 
  the 
  other 
  side 
  is 
  prevented 
  from 
  contracting, 
  

   there 
  will 
  exist 
  a 
  state 
  of 
  constraint 
  from 
  which 
  the 
  surface 
  is 
  endea- 
  

   vouring 
  to 
  free 
  itself 
  by 
  forcing 
  the 
  roller 
  back. 
  

  

  Besides 
  the 
  relative 
  softness 
  of 
  the 
  materials, 
  the 
  curvature 
  of 
  the 
  

   roller 
  will 
  affect 
  the 
  lateral 
  extension 
  both 
  of 
  the 
  roller 
  and 
  the 
  plane 
  at 
  

   the 
  point 
  of 
  contact, 
  so 
  that 
  if 
  the 
  roller 
  and 
  the 
  plane 
  were 
  of 
  the 
  same 
  

   material 
  there 
  would 
  still 
  be 
  slipping. 
  This 
  would 
  not 
  be 
  the 
  case, 
  how- 
  

   ever, 
  between 
  two 
  wheels 
  of 
  the 
  same 
  diameter 
  and 
  material 
  rolling 
  in 
  

   contact. 
  

  

  Such 
  is 
  a 
  short 
  sketch 
  of 
  the 
  subject 
  of 
  the 
  paper, 
  a 
  considerable 
  part 
  

   of 
  which 
  is 
  devoted 
  to 
  the 
  examination 
  and 
  illustration 
  of 
  the 
  exact 
  

   manner 
  in 
  which 
  the 
  deformation 
  at 
  the 
  point 
  of 
  contact 
  occurs, 
  and 
  the 
  

   influence 
  of 
  friction 
  upon 
  it. 
  The 
  latter 
  part 
  of 
  the 
  paper 
  contains 
  an 
  

   account 
  of 
  numerous 
  experiments, 
  and 
  their 
  results, 
  which 
  were 
  under- 
  

   taken 
  as 
  part 
  of 
  this 
  investigation. 
  

  

  The 
  first 
  series 
  of 
  experiments 
  relate 
  to 
  the 
  resistance 
  which 
  an 
  iron 
  

   roller 
  experiences 
  on 
  surfaces 
  of 
  different 
  hardness. 
  Cast 
  iron, 
  glass, 
  brass, 
  

   boxwood, 
  and 
  india-rubber 
  were 
  tried. 
  Extreme 
  care 
  was 
  taken 
  to 
  make 
  the 
  

   roller 
  and 
  the 
  surfaces 
  true 
  ; 
  and 
  this 
  was 
  so 
  far 
  successful 
  that 
  on 
  cast 
  iron 
  

   the 
  roller 
  would 
  roll 
  in 
  either 
  direction 
  when 
  the 
  surface 
  had 
  an 
  inclination 
  

   of 
  one 
  in 
  five 
  thousand, 
  or, 
  roughly, 
  a 
  foot 
  in 
  a 
  mile. 
  Comparing 
  the 
  

   different 
  surfaces, 
  we 
  see 
  that 
  the 
  resistance 
  increases 
  with 
  the 
  softness, 
  

   although 
  apparently 
  not 
  in 
  the 
  simple 
  proportion 
  ; 
  on 
  boxwood 
  the 
  resist- 
  

   ance 
  is 
  nearly 
  double 
  as 
  great 
  as 
  on 
  the 
  harder 
  surfaces, 
  and 
  on 
  india- 
  

   rubber 
  from, 
  six 
  to 
  ten 
  times 
  as 
  great. 
  

  

  The 
  second 
  series 
  of 
  experiments 
  were 
  to 
  ascertain 
  the 
  actual 
  extent 
  of 
  

   slipping 
  on 
  india-rubber, 
  both 
  with 
  a 
  cast-iron 
  roller 
  and 
  also 
  with 
  an 
  

   india-rubber 
  tire 
  glued 
  on 
  to 
  the 
  roller, 
  and 
  rolled 
  on 
  hard 
  surfaces 
  and 
  

   on 
  plates 
  of 
  india-rubber 
  of 
  different 
  thicknesses. 
  

  

  These 
  experiments 
  bear 
  out 
  the 
  arguments 
  expressed 
  in 
  the 
  first 
  part 
  

   of 
  the 
  paper 
  ; 
  in 
  fact 
  the 
  arguments 
  were 
  based 
  on 
  the 
  experiments. 
  

   There 
  is 
  no 
  intention 
  to 
  imply 
  that 
  the 
  whole 
  of 
  the 
  resistance 
  to 
  rolling 
  

   is 
  in 
  all 
  cases 
  due 
  to 
  the 
  causes 
  already 
  mentioned. 
  Under 
  ordinary 
  cir- 
  

   cumstances 
  the 
  irregularities 
  of 
  the 
  surfaces 
  and 
  the 
  crushing 
  of 
  the 
  

   material 
  beneath 
  the 
  roller 
  are 
  the 
  chief 
  causes. 
  And, 
  besides 
  these, 
  two 
  

   other 
  causes 
  are 
  discussed 
  in 
  the 
  paper 
  as 
  having 
  been 
  brought 
  to 
  light 
  

   by 
  the 
  experiment, 
  viz. 
  the 
  communication 
  of 
  heat 
  between 
  the 
  compressed 
  

   material 
  and 
  that 
  which 
  surrounds 
  it, 
  which 
  prevents 
  the 
  material 
  im- 
  

  

  