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no  common  opinion  as  to  the  period  of  time  which
must  elapse  before  the  effect  of  an  increase  in  the
volume  of  currency  becomes  apparent  in  rising
prices.  A  recent  study  10  of  English  experience  in
this  particular  made  by  Professor  J.  Shield  Nicholson ­
  of  the  University  of  Edinburgh  led  to  the  conclusion ­
  that  the  period  in  which  the  increase  in  currency ­
  worked  itself  out  in  higher  prices  —  happily
described  as  “  the  period  of  incubation  ”  was  about
five  months.  A  similar  analysis 11  of  Canadian  experience ­
  by  Mr.  W.  C.  Clark  of  Kingston,  Ontario,
established  the  period  of  incubation  for  that  country
to  be  six  months  —  a  difference  “  one  would  expect
in  a  country  less  densely  populated  and  less  highly
industrialized,  as  Canada  is.”  For  the  United
States,  Professor  Irving  Fisher,  examining  the  figures ­
  up  to  the  time  of  our  entry  into  the  war,  finds
that  after  the  middle  of  1915  ‘‘a  change  in  price
level  follows  a  change  in  total  money  after  a  lag  of
about  two  months,”  12  and  in  a  later  resume  this  is
restated  as  “  a  lag  in  this  country  of  less  than  two
months/’  13
It  is  not  unlikely  that  as  fuller  data  become  available ­
  Professor  Fisher’s  computation  will  indicate  a
longer  lag  than  the  original  estimate,  as  did  appar-10
  “  Statistical  Aspects  of  Inflation  ”  in  Journal  of  the  Royal
Statistical  Society,  July,  1917.
11  Clark,  “  Inflation  and  Prices  ”  in  Journal  of  the  Canadian
Bankers’  Association,  January,  1918.
12  “  The  Equation  of  Exchange  for  1916  ”  in  American  Economic ­
  Review,  December,  1917,  p.  937.
13  “  Some  Contributions  of  the  War  to  our  Knowledge  of
Money  and  Prices  ”  (abstract)  in  American  Economic  Review,
Supplement,  March,  1918,  p.  258.