and four of the Quadrivium. The three of the Trivium concerned the
use of speech; they were Grammar, Rhetoric, and Logic. The four of
the Quadrivium concerned number and measure; they were Arithmetic,
Geometry, Music; and Astronomy, which led up straight to God.
Advance to Music might be represented in the student's mind by his
reaching to a sense of the harmonious relation of all his studies,
which, so to speak, lived in his mind as a single well-proportioned
thought.

In 1652 Dr. Petty was sent to Ireland as physician to the army of
the Commonwealth. While there his active mind observed that the
Survey on which the Government had based its distribution of
fortified lands to the soldiers had been "most inefficiently and
absurdly managed." He obtained the commission to make a fresh
Survey, which he completed accurately in thirteen months, and by
which he obtained in payments from the Government and from other
persons interested ten thousand pounds. By investing this in the
purchase of soldiers' claims, he secured for himself an Irish estate
of fifty thousand acres in the county of Kerry, opened upon it mines
and quarries, developed trade in timber, and set up a fishery. John
Evelyn said of him "that he had never known such another genius, and
that if Evelyn were a prince he would make Petty his second
councillor at least." Henry Cromwell as Lord Deputy in Ireland made
Petty his secretary.

Petty's Maps were printed in 1685, two years before his death, as
"Hiberniae Delineatio quoad hactenus licuit perfectissima;" a
collection of thirty-six maps, with a portrait of Sir William Petty,
a work answering to its description as the most perfect delineation
of Ireland that had up to that time been obtained. There is a