Thank you, Nicholas and Mason, for pursuing this and providing the 
quoted material.

Apart from the time discounting, I was struck by the risk 
discounting.  In Chapter IV around par 22, Petty notes that the years 
purchase reflecting value in England would be lessened in Ireland on 
account of frequent rebellions and thieves and robbers reacting to 
landlords' presence.  One must wonder whether England's later 20th 
century departures from Ireland (rather dragged out afther the rising 
of 1916) and the Indian sub-continent (rather more hurried after 
WWII), A) were predictable under Petty's calculus that the cost of 
"ownership" outweighed the revenues, and B) were more  motivated by 
economics than by post-imperial enlightenment.

Scott Cullen