1 The Birth of Science - MSRI

98 4. Scientific Technology
pedem) and that classical authors, including some of the best-known, mention
it many times, even giving fairly detailed explanations of how it was
done, 58 this would seem to be an open-and-shut question. Yet even here
the primitivist position has had its defenders. 59
From our point of view, a particularly interesting testimonium is that of
the pseudo-Aristotelian Mechanics, giving a “scientific” — and correct — page 136
explanation of how close-hauled sailing works. 60 Here everything indicates
that practice preceded theory, 61 but the need to include even sailing
techniques into the framework of mechanics is an interesting example of
the interaction between science and craft.
To sail the open seas, more than an approximate knowledge of the cardinal
points (obtainable from a compass if the skies are overcast) it is essential
to have
– a coordinate system, that is, a scientific theory of geography;
– reliable charts; and
– a method to locate the ship with respect to the coordinate system.
With these theoretical instruments, even without a compass, one can correct
for deviations from course caused by currents, leeway, storms and
poor orientation on starless nights. By contrast, if one has a compass but
is not able to determine the ship’s position, the inevitable errors accumulate
uncorrected and the ship necessarily goes off course. The usefulness of
the compass is that it reduces the magnitude of the necessary corrections,
but the corrections are always needed and yet cannot be made without the
theoretical instruments listed above.
Spherical coordinates were relearned when a copy of Ptolemy’s Geography
reached the West, in the fifteenth century. The recovery of Hellenistic
navigation instruments, including the plane astrolabe, 62 allowed mariners
to determine latitude on the open sea through astronomical observations. 63
58 See [Casson: SS], pp. 273–278, where several sources are quoted. We mention only Lucian,
Navigium, 9; Pliny, Natural history, II, 128.
59 The relevant article in the History of technology dismisses the skeptics and states that Roman
ships could beat to windward, though only in “the most limited sense” ([Lethbridge], p. 574) until
the invention of the lateen sail — of unknown date but probably due “to the Graeco-Romans” —
made the task easy (ibid., p. 583–584).
60 Pseudo-Aristotle, Mechanica, 851b, 7–14. See [Casson: SS], p. 276, footnote 24, which points out
that the explanation is correct.
61 It is interesting that Philostratus attributes the discovery of techniques for windward sailing to
the Phoenicians (Philostratus, Heroicus, 1, 2).
62 That the plane astrolabe was a Hellenistic instrument known to Ptolemy was established in
[Neugebauer: EHA]. Until then it was thought that its invention dated from much later.
63 Measuring longitude is much harder, but one can do without it by first reaching the desired
latitude and then sailing along that parallel to one’s destination.
Revision: 1.14 Date: 2002/10/24 04:25:47