1 The Birth of Science - MSRI

304 11. The Age-Long Recovery
(finally!) gave an explanation for how telescopes work, though it seems
that the instrument did not exist then. Since the book came out in 1611,
when telescopes were the order the day thanks to Galileo’s discoveries of
the previous year, doubts have been cast on the date of writing stated by page 375
Bartolo, but what is unarguable is that around 1590 the theory, if not yet
the practice, of the telescope was spreading around Europe, because the
second edition of Della Porta’s Magia naturalis (1589) makes very precise
references to it. 55
It seems that the development of optics was plagued by amazing bad
luck: the “Ancients” knew how to make good lenses but did not know
what to make of them and kept them as baubles, 56 later intellectuals —
not just Leonardo and Fracastoro, 57 but also Roger Bacon and Grosseteste
centuries earlier — knew many uses for them, yet could not build them
and had never even seen such things. Some medieval manuscripts even
show astronomers looking at the sky through long tubes; the incongruency
has been addressed by postulating that these were empty sightingtubes!
59 Consider that Bacon, in the fifth book of the Opus Maius, waxed
enthusiastic about the Ancients’ ability to enlarge small objects and to
bring faraway ones close, using appropriate configurations of lenses and
mirrors — though he himself is unable to present a reasonable theory even
in the case of a single lens. Consider the lucid account, in Grosseteste’s On
the rainbow (ca. 1230), of the possibility of using refraction phenomena to
build magnifiers and telescopes:
The main parts [of optics] are three, according to the ways in which
the rays can reach what is seen. Either the course of the ray is straight,
through a uniform transparent medium lying between the viewer
and the object seen; or its course is straight toward . . . a mirror,
in which it is reflected and so reaches the object seen; or the ray
goes through several transparent media of different natures, at the
boundaries of which it bends at an angle, thus reaching the object
55
We met Della Porta when discussing the resurrection of the steam engine recorded by Heron,
and we will meet him again in connection with Philo of Byzantium’s thermoscope. This playwright
and student of the classics alludes in his works to many other objects of “modern” technology, such
as the “magic lantern” (which had also been a subject for Alhazen).
56
See page 241.
57
See page 301.
59
In [Price: Instruments], p. 595, two such illustrations are redrawn, one from a Saint Gall
manuscript of 982 and one from an unspecified thirteenth-century manuscript. No source is given.
Price gallantly allows as how the idea that these are depictions of telescopes “cannot be summarily
discarded merely because of the great improbability of the invention having been made so early”
(p. 593), and then tacitly discards it. In fact the illustrations may be representatives of a residual
iconographic tradition that was no longer understood.
Revision: 1.11 Date: 2003/01/06 07:48:20