﻿408 
  Rowland 
  — 
  The 
  Highest 
  Aim 
  of 
  the 
  Physicist. 
  

  

  upon 
  assumptions 
  more 
  or 
  less 
  reasonable 
  but 
  always 
  assump- 
  

   tions. 
  A 
  mathematical 
  investigation 
  always 
  obeys 
  the 
  law 
  of 
  

   the 
  conservation 
  of 
  knowledge 
  : 
  we 
  never 
  get 
  out 
  more 
  from 
  

   it 
  than 
  we 
  put 
  in. 
  The 
  knowledge 
  may 
  be 
  changed 
  in 
  form, 
  

   it 
  may 
  be 
  clearer 
  and 
  more 
  exactly 
  stated, 
  but 
  the 
  total 
  amount 
  

   of 
  the 
  knowledge 
  of 
  nature 
  given 
  out 
  by 
  the 
  investigation 
  is 
  

   the 
  same 
  as 
  we 
  started 
  with. 
  Hence 
  we 
  can 
  never 
  predict 
  the 
  

   result 
  in 
  the 
  case 
  of 
  velocities 
  beyond 
  our 
  reach, 
  and 
  such 
  cal- 
  

   culations 
  as 
  the 
  velocity 
  of 
  the 
  cathode 
  rays 
  from 
  their 
  electro- 
  

   magnetic 
  action 
  has 
  a 
  great 
  element 
  of 
  uncertainty 
  which 
  we 
  

   should 
  do 
  well 
  to 
  remember. 
  

  

  Indeed, 
  when 
  it 
  comes 
  to 
  exact 
  knowledge, 
  the 
  limits 
  are 
  far 
  

   more 
  circumscribed. 
  

  

  Plow 
  is 
  it, 
  then, 
  that 
  we 
  hear 
  physicists 
  and 
  others 
  constantly 
  

   stating 
  what 
  will 
  happen 
  beyond 
  these 
  limits? 
  Take 
  veloci- 
  

   ties, 
  for 
  instance, 
  such 
  as 
  that 
  of 
  a 
  material 
  body 
  moving 
  with 
  

   the 
  velocity 
  of 
  light. 
  There 
  is 
  no 
  known 
  process 
  by 
  which 
  

   such 
  a 
  velocity 
  can 
  be 
  obtained 
  even 
  though 
  the 
  body 
  fell 
  from 
  

   an 
  infinite 
  distance 
  upon 
  the 
  largest 
  aggregation 
  of 
  matter 
  in 
  the 
  

   Universe. 
  If 
  we 
  electrify 
  it, 
  as 
  in 
  the 
  cathode 
  rays, 
  its 
  prop- 
  

   erties 
  are 
  so 
  changed 
  that 
  the 
  matter 
  properties 
  are 
  completely 
  

   masked 
  by 
  the 
  electromagnetic. 
  

  

  It 
  is 
  a 
  common 
  error 
  which 
  young 
  physicists 
  are 
  apt 
  to 
  fall 
  

   into 
  to 
  obtain 
  a 
  law, 
  a 
  curve 
  or 
  a 
  mathematical 
  expression 
  fur 
  

   given 
  experimental 
  limits 
  and 
  then 
  to 
  apply 
  it 
  to 
  points 
  outside 
  

   those 
  limits. 
  This 
  is 
  sometimes 
  called 
  extrapolation. 
  Such 
  a 
  

   process, 
  unless 
  carefully 
  guarded, 
  ceases 
  to 
  be 
  a 
  reasoning 
  

   process 
  and 
  becomes 
  one 
  of 
  pure 
  imagination 
  specially 
  liable 
  

   to 
  error 
  when 
  the 
  distance 
  is 
  too 
  great. 
  

  

  But 
  it 
  is 
  not 
  my 
  purpose 
  to 
  enter 
  into 
  detail. 
  What 
  I 
  have 
  

   given 
  suffices 
  to 
  show 
  how 
  little 
  we 
  know 
  of 
  the 
  profounder 
  

   questions 
  involved 
  in 
  our 
  subject. 
  

  

  It 
  is 
  a 
  curious 
  fact 
  that, 
  having 
  minds 
  tending 
  to 
  the 
  infinite^ 
  

   with 
  imaginations 
  unlimited 
  by 
  time 
  and 
  space, 
  the 
  limits 
  of 
  

   our 
  exact 
  knowledge 
  are 
  very 
  small 
  indeed. 
  In 
  time 
  we 
  are 
  

   limited 
  by 
  a 
  few 
  hundred 
  or 
  possibly 
  thousand 
  years: 
  indeed 
  

   the 
  limit 
  in 
  our 
  science 
  is 
  far 
  less 
  than 
  the 
  smaller 
  of 
  these 
  

   periods. 
  In 
  space 
  w^e 
  have 
  exact 
  knowledge 
  limited 
  to 
  por- 
  

   tions 
  of 
  our 
  earth's 
  surface 
  and 
  a 
  njile 
  or 
  so 
  below 
  the 
  surface, 
  

   together 
  with 
  what 
  little 
  we 
  can 
  learn 
  from 
  looking 
  through 
  

   powerful 
  telescopes 
  into 
  the 
  space 
  beyond. 
  In 
  temperature 
  

   our 
  knowledge 
  extends 
  from 
  near 
  the 
  absolute 
  zero 
  to 
  that 
  of 
  

   the 
  sun 
  but 
  exact 
  knowledge 
  is 
  far 
  more 
  limited. 
  In 
  pressures 
  

   we 
  go 
  from 
  the 
  Crookes 
  vacuum 
  still 
  containing 
  myriads 
  of 
  

   flying 
  atoms 
  to 
  pressures 
  limited 
  by 
  the 
  strength 
  of 
  steel 
  but 
  

   still 
  very 
  minute 
  compared 
  w^tli 
  the 
  pressures 
  at 
  the 
  center 
  of 
  

   the 
  earth 
  and 
  sun, 
  where 
  the 
  hardest 
  steel 
  would 
  flow 
  like 
  the 
  

  

  