st be added to or
diminished in proportion to the size of the farm: and this applies
only if the land is all of the same character, for if part of it is of
a kind which cannot be ploughed, as for example very rocky, or on
a steep hillside, there is that much less necessity for teams and
teamsters. I pass over the fact that Cato's example of a farm of two
hundred and forty jugera is neither a fair nor a comparable unit.[78]
The true unit for comparison of farms is a centuria, which contains
two hundred jugera, but if one deducts forty jugera, or one-sixth,
from Cato's two hundred and forty jugera, I do not see how in applying
this rule one can deduct also one-sixth of his thirteen slaves; or,
even if we leave out the overseer and the housekeeper, how one can
deduct one-sixth of eleven slaves. Again, Cato says that one should
have fifteen slaves for one hundred jugera of vineyard, but suppose
one had a _centuria_ half in vines and half in olives, then, according
to Cato's rule, one would require two overseers and two housekeepers,
which is absurd. Wherefore it is necessary to find another measure
than Cato's for determining the number of slaves, and I myself think
better of Saserna's rule, which is that for each jugerum it suffices
to provide four days work of one hand. Yet, if this was a good rule
on Saserna's farm in Gaul, it might not apply on a mountain farm in
Liguria. In fine you will best determine what number of slaves and
what other equipment you will require if you diligently consider
three things, that is to say, what kind of farms are there in your
neighbourhood, how large are they, and how many hands are engaged in
cultivating them, and you should add to or subtract from that number
in proportion as you take up more or less work. For nature gave us two
schools of agriculture, which are experience and imitation. The most
ancient farmers established many principles by experiment and their
descendants for the most part have simply imitated them. We should
do both these things: imitate others and on our own account make
experiments, following always some principle, not chance:[79] thus we
might work our trees deeper or not so deep as others do to see what
the effect would be. It was with such intelligent curiosity that some
farmers first cultivated their vines a second and a third time, and
deferred grafting the figs from spring to summer."

_Of draught animals_

XIX. In respect of those instruments of agricu