﻿JOURNAL 
  

  

  OF 
  THE 
  

  

  WASHINGTON 
  ACADEMY 
  OF 
  SCIENCES 
  

  

  Vol. 
  12 
  April 
  4, 
  1922 
  No. 
  7 
  

  

  PHYSICS. 
  — 
  Note 
  on 
  a 
  general 
  method 
  for 
  determining 
  properties 
  of 
  

   matter.^ 
  Mayo 
  D. 
  Hersey, 
  Massachusetts 
  Institute 
  of 
  Tech- 
  

   nology. 
  

   Physical 
  properties 
  of 
  substances, 
  for 
  example, 
  thermal 
  and 
  elec- 
  

   trical 
  conductivity, 
  density, 
  viscosity, 
  and 
  surface 
  tension, 
  are 
  usually 
  

   determined 
  by 
  one 
  or 
  the 
  other 
  of 
  the 
  two 
  following 
  methods. 
  (1) 
  

   Absolute 
  measurement, 
  involving 
  comparatively 
  expensive 
  apparatus 
  

   and 
  detailed 
  mathematical 
  analysis. 
  (2) 
  Relative 
  measurement 
  

   in 
  terms 
  of 
  the 
  properties 
  of 
  a 
  standard 
  sample. 
  This 
  method 
  is 
  

   comparatively 
  simple 
  and 
  economical, 
  but 
  has 
  almost 
  always 
  been 
  

   restricted 
  in 
  the 
  past 
  to 
  those 
  few 
  phenomena 
  where 
  the 
  desired 
  prop- 
  

   erty 
  is 
  directly 
  proportional 
  to 
  the 
  observed 
  action, 
  or 
  to 
  some 
  definite 
  

   function 
  of 
  the 
  observed 
  action 
  which 
  can 
  be 
  written 
  down 
  in 
  advance 
  

   of 
  the 
  experiment. 
  It 
  is 
  the 
  object 
  of 
  the 
  present 
  paper 
  to 
  indicate 
  

   a 
  third 
  category 
  of 
  experiments 
  which 
  should 
  be 
  available 
  for 
  deter- 
  

   mining 
  properties 
  of 
  matter, 
  much 
  less 
  restricted 
  in 
  character 
  than 
  

   those 
  mentioned 
  above; 
  and 
  to 
  formulate 
  a 
  general 
  method 
  for 
  in- 
  

   terpreting 
  the 
  obser\'ations. 
  

  

  This 
  third 
  group 
  of 
  phenomena 
  are 
  characterized 
  by 
  the 
  fact 
  that 
  

   the 
  observed 
  action 
  will 
  not 
  be 
  directly 
  proportional 
  to 
  the 
  property 
  

   in 
  question, 
  nor 
  even 
  uniquely 
  determined 
  by 
  it, 
  and 
  it 
  is 
  quite 
  imma- 
  

   terial 
  if 
  the 
  details 
  of 
  the 
  phenomenon 
  are 
  too 
  irregular 
  to 
  be 
  analyzed 
  

   mathematically. 
  The 
  proposed 
  method 
  for 
  interpreting 
  such 
  ob- 
  

   serv^ations 
  consists 
  merely 
  in 
  applying 
  the 
  principle 
  of 
  dynamical 
  

   similarity 
  (or 
  physical 
  similarity) 
  backwards. 
  Instead 
  of 
  employing 
  

   this 
  principle 
  to 
  predict 
  the 
  course 
  of 
  a 
  phenomenon, 
  when 
  the 
  proper- 
  

   ties 
  of 
  matter 
  involved 
  are 
  altered 
  in 
  a 
  known 
  manner, 
  it 
  is 
  now 
  pro- 
  

   posed 
  to 
  turn 
  it 
  around, 
  and 
  deduce 
  the 
  relative 
  magnitudes 
  of 
  the 
  

   properties 
  of 
  matter 
  involved 
  in 
  two 
  successive 
  experiments, 
  by 
  ob- 
  

   serving 
  the 
  phenomena 
  in 
  both 
  cases. 
  

  

  This 
  possibility 
  must 
  immediately 
  suggest 
  itself 
  to 
  anyone 
  familiar 
  

   with 
  the 
  principle 
  of 
  similarity 
  or 
  the 
  theory 
  of 
  dimensions, 
  and 
  it 
  

  

  ' 
  Received 
  January 
  24, 
  1922. 
  

  

  167 
  

  

  