1 The Birth of Science - MSRI

312 11. The Age-Long Recovery
water thus collected was weighed, after each descent, on a very accurate
balance; the differences and ratios of these weights gave us
the differences and ratios of the times, and this with such accuracy
that although the operation was repeated many, many times, there
was no appreciable discrepancy in the results. 85
Galileo understood well how important it was, in order to rebuild the
experimental basis of ancient science, to find a replacement for the precise
water clocks whose technology had long ago been lost. But the fact that
his measurements, though repeated so often, never showed discrepancies
cannot but make a modern physicist wonder. Galileo’s description of his
timepiece, so more rudimentary to Ctesibius’ clocks, strengthens the suspicion
that measurements of time via buckets and glasses were complemented
in other ways. A sentence a few lines before the quoted passage,
in the description of the experimental setup, provides a clue to this “complementation”:
We repeated [the ball’s run] several times in order to be sure of the
elapsed time, and it never presented a deviation exceeding one tenth
of a heartbeat. 86
Evidently, the pulse was the most commonly used clock. It is worth
pausing to consider how far we still were, in spite of Galileo’s efforts,
from the refined measuring instruments (the basis of any true experimental
method) that had once allowed Herophilus to study scientifically the
heartbeat and to use the theory thus built in making diagnostics. 87
In spite of its mathematical and technological limitations, the recovery
work carried out by Galileo was extraordinary, especially in terms of
methodology. He borrowed from ancient science the humility of the scientific
method, which is content with tackling well-circumscribed problems
(such as motion under gravity or hydrostatics) through the tools of
mathematics and experimentation, and resists the temptation to pursue
85 Galileo Galilei, Discorsi e dimostrazioni. . . , third day, at Salviati’s first turn after Corollary I =
[Galileo: Opere], vol. VIII, p. 213 (Crew and de Salvio translation).
86 Ibid.
87 See pages 123–126 and 132. This observation may seem contrary to the statement, contained
in a letter of Vincenzo Viviani to Leopoldo de’ Medici (published in [Galileo: Opere], vol. XIX,
pp. 647–659), that Galileo thought of using a pendulum to measure the heartbeat. But of course a
pendulum only lets one measure intervals of time equal to several periods or more, which is why
Galileo used not a pendulum but a water clock (besides his pulse and possibly other methods) for
the experiments on gravity. The frequency of the pulse can be obtained from the overall time of
many beats (which does lend itself to measurements with a pendulum), but this will not yield the
ratio between systolic and diastolic intervals, which had been studied by Herophilus. To measure
the overall time of many systoles or diastoles one must have a stopwatch that can be stopped and
started at will, as is the case with a water clock.
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