William Petty Treatise of Taxes chap IV
The following is a cut and paste from the OLL site
http://oll.libertyfund.org/index.php?option=com_staticxt&staticfile=show.php&title=1677&search=%22grandfather%22&layout=html#chapter_30565

19. Having found the Rent or value of the usus fructus per annum, the
question is, how many years purchase (as we usually say) is the Fee simple
naturally worth? If we say an infinite number, then an Acre of Land would
be equal in value to a thousand Acres of the same Land; which is absurd,
an infinity of unites being equal to an infinity of thousands. Wherefore
we must pitch upon some limited number, and that I apprehend ‖ to be
the number of years, which I conceive one man of fifty years old, another
of twenty eight, and another of seven years old, all being alive together
may be thought to live1 ; that is to say, of a Grandfather, Father, and
Childe; few men having reason to take care of more remote Posterity: for
if a man be a great Grandfather, he himself is so much the nearer his end,
so as there are but three in a continual line of descent usually
co-existing together; and as some are Grandfathers at forty years, yet as
many are not till above sixty, and sic de cæteris.

20. Wherefore I pitch the number of years purchase, that any Land is
naturally worth, to be the ordinary extent of three such persons their
lives. Now in England we esteem three lives equal to one and twenty years,
and consequently the value of Land, to be about the same number of years
purchase Possibly if they thought themselves mistaken in the one, (as the
observator on the Bills of Mortality thinks they are2 ) they would alter
in the other, unless the consideration of the force of popular errour and
dependance of things already concatenated, did hinder them.

21. This I esteem to be the number of years purchase where Titles are
good, and where there is a moral certainty of enjoying the purchase. But
in other Countreys Lands are worth nearer thirty years purchase, by reason
of the better Titles, more people, and perhaps truer opinion of the value
and duration of three lives.

22. And in some places, Lands are worth yet more years purchase by reason
of some special honour, pleasures, priviledge or jurisdiction annexed unto
them.

23. On the other hand, Lands are worth fewer years purchase (as in
Ireland) for the following reasons, which I have here set down, as unto
the like whereof the cause of the like cheapness in anyother place may be
imputed.

First, In Ireland, by reason of the frequent Rebellions, (in which if you
are conquered, all is lost; or if you conquer, yet you are subject to
swarms of thieves and robbers) and the envy which precedent missions of
English have against the ‖ subsequent perpetuity it self is but
forty years long, as within which time some ugly disturbance hath hitherto
happened almost ever since the first coming of the English thither.

24. 2. The Claims upon Claims which each hath to the others Estates, and
the facility of making good any pretence whatsoever by the favour of some
one or other of the many Governours and Ministers which within forty years
shall be in power there; as also by the frequency of false testimonies,
and abuse of solemn Oaths.

25. 3. The paucity of Inhabitants, there being not above the ⅕th
part so many as the Territory would maintain, and of those but a small
part do work at all, and yet a smaller work so much as in other Countreys.

26. 4. That a great part of the Estates, both real and personal in
Ireland, are owned by Absentees, and such as draw over the profits raised
out of Ireland refunding nothing; so as Ireland exporting more then it
imports doth yet grow poorer to a paradox.

27. 5. The difficulty of executing justice, so many of those in power
being themselves protected by Offices, and protecting others. Moreover,
the number of criminous and indebted persons being great, they favour
their like in Juries, Offices, and wheresoever they can: Besides, the
Countrey is seldom† enough to give due encouragement to profound
Judges and Lawyers, which makes judgements very casual; ignorant men being
more bold to be apt and arbitrary, then such as understand the dangers of
it. But all this with‡ a little care in due season might remedy, so
as to bring Ireland in a few years to the same level of values with other
places; but of this also elsewhere more at large, for in the next place we
shall come to Usury

Nicholas Theocarakis