William Petty, born on the 26th of May, 1623, was the son of a
clothier at Romsey in Hampshire. After education at the Romsey
Grammar School, he continued his studies at Caen in Normandy. There
he supported himself by a little trade while learning French, and
advancing his knowledge of Greek, Latin, Mathematics, and much else
that belonged to his idea of a liberal education. His idea was
large. He came back to England, and had for a short time a place in
the Navy; but at the age of twenty he went abroad again, and was
away three years, studying actively at Utrecht, Leyden, and
Amsterdam, and also in Paris. In Paris he assisted Thomas Hobbes in
drawing diagrams for his treatise on optics. At the age of twenty-
four Petty took out a patent for the invention of a copying machine.
It was described in a folio pamphlet "On Double Writing." That was
in 1647, in Civil War time, and although Petty followed Hobbes in
his studies, he did not share the philosopher's political opinions,
but held with the Parliament. In 1648 he added to his former
pamphlet a "Declaration concerning the newly invented Art of Double
Writing."

Samuel Hartlib, the large-hearted Pole, who in those days spent his
worldly means in England for the advancement of agriculture and of
education, and other aids to the well-being of a nation, had caused
Milton to write his letter on education, as has been shown in the
Introduction to the hundred and twenty-first volume of this Library,
which contains that Letter together with Milton's Areopagitica.
Young Petty's first published writing was a Letter to Hartlib on
Education, entitled "The Advice of W. P. to Mr. Samuel Hartlib for
the Advancement of some Particular Parts of Learning." This