THE INVENTION OF INVENTION^47spectacles that help one to see well, an art that is one of the best and most
necessary in the world. And that is such a short time ago that a new art that
never before existed was invented. ... I myself saw the man who discov
ered and practiced it and I talked with him.^4These convex lenses were obviously not uniform or of what we would
call prescription quality. But here medieval optical technology, however
primitive, was saved by the nature of the difficulty: the lenses to cor
rect presbyopia do not have to be extremely accurate. Their function
is primarily to magnify, and although some magnify more than others,
just about any and all will help the user. This is why people will occa
sionally borrow glasses in a restaurant to read the menu, and why five-
and-dime stores can put out boxes of such spectacles for sale. The
buyer simply tries a few and picks the most suitable. Myopes (short
sighted people) cannot do that.
That was the beginning. By the middle of the fifteenth century, Italy,
particularly Florence and Venice, was making thousands of spectacles,
fitted with concave as well as convex lenses, for myopes as well as pres-
byopes. Also, the Florentines at least (and presumably others) under
stood that visual acuity declines with age and so made the convex
lenses in five-year strengths and the concave in two, enabling users to
buy in batches and change with time.
Eyeglasses made it possible to do fine work and use fine instruments.
But also the converse: eyeglasses encouraged the invention of fine in
struments, indeed pushed Europe in a direction found nowhere else.
The Muslims knew the astrolabe, but that was it. The Europeans went
on to invent gauges, micrometers, fine wheel cutters—a battery of
tools linked to precision measurement and control. They thereby laid
the basis for articulated machines with fitted parts.
Close work: when other civilizations did it, they did it by long ha
bituation. The skill was in the hand, not the eye-and-tool. They
achieved remarkable results, but no piece was like any other; whereas
Europe was already moving toward replication—batch and then mass
production. This knowledge of lenses, moreover, was a school for fur
ther optical advances, and not only in Italy. Both telescope and micro
scope were invented in the Low Countries around 1600 and spread
quickly from there.
Europe enjoyed a monopoly of corrective lenses for three to four
hundred years. In effect they doubled the skilled craft workforce, and
more than doubled it if one takes into account the value of experience.^5
- The mechanical clock. Another banality, so commonplace that we