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GASSENDI (GASSEND), PIERRE (b. Champtercier,
France, 22 January 1592; d. Paris, France, 24 October
1655), philosophy, astronomy, scholarship.
the phenomenon of the tides as a proof of the motion
of the earth. As was well known, the periodicity of
the tides does not correspond to that of the diurnal
movement, and Descartes did not make this mistake.14
On one point—and it is an important one—Gassendi
was more successful than Galileo: he correctly
stated the principle of inertia. The experiment
of the De motu impresso a motore translato, performed
in 1640 in Marseilles, overthrew the argument of
Copernicus' opponents against the movement of the
earth. Gassendi arranged to have a weight dropped
from the top of a vertical mast on a moving ship in
order to demonstrate that it fell at the foot of the
mast and not behind it, thus sharing in its fall the
forward motion of the ship. Galileo considered the
experiment unnecessary; he foresaw the result by
reasoning.15 Others, notably Bruno, had already
spoken of it. But Gassendi understood that the composition
of motions is a universal phenomenon: Every
movement impressed on a body in motion in any
direction whatsoever persists in Democritean space,
which has neither up nor down. Motion is, in itself,
a physical state, a measurable quantity, not—as the
Scholastics maintained—the change from one state
to another. It changes only through the interposition
of another movement or of an obstacle.
Furthermore, Gassendi also corrected the formulation
given by Kepler, for whom inertia was a tendency
to rest: in classical physics, inertia is indifference to
both motion and rest. On this point, Gassendi was
guided by Galileo's experiments on the pendulum,
in which motion is maintained without any supplementary
impetus. In addition, Kepler's idea of
magnetic effluents or forces gave him an intimation
of the existence of universal attraction or, rather,
universal interaction—although he was no more successful
than Descartes in conceiving its transmission
otherwise than by contact.16
Gassendian atoms and Cartesian subtle matter
belong, as has been seen, to a single period of thought.
Moreover, the idea of inertia was common to Beeckman,
Gassendi, and Descartes, who all knew each
other, and we know that Newton read Gassendi, as
did Boyle and Barrow.
In 1650, on a mountain near Toulon, another experiment
repeated the famous one of the Puy-de-Dôme.17
Gassendi fully appreciated the value of Pascal's work.
But the latter, in the Équilibre des liqueurs,18
speaks
indiscriminately of “weight and pressure of the air,”
whereas, guided by the corpuscular picture and not
by the hydrostatic scheme referred to in Pascal's title,
Gassendi could differentiate weight (which is constant
for a given mass of air) from pressure (which
varies according to the state of agitation, dilation, or
contraction of this same mass). It is variations in
pressure that affect the barometer and that measure
not only the approximate height of the “column of
air” but also the changes of state of the atmosphere,
which are capable of influencing subsequent weather
conditions. Of course, the barometric vacuum proves
that the natural vacuum is not impossible; but what
happens in the tube depends only on what happens
outside. Koyré rightly points out that in this regard
Gassendi anticipated Boyle, who read him closely and
regretted not having done so earlier.19
Gassendi applied his empirical and experimental
sagacity to other fields, often in collaboration with
Mersenne. Together they estimated the speed of
sound as 1,038 feet per second, a passable approximation
for the time.20 Physiology and dissection also
interested Gassendi, as did all of natural history.
However, he never completely renounced a false observation
made at Aix in his youth when Payen made
him “see” a communication between the two parts
of the heart; but at least he esteemed Harvey and
Pecquet. Numismatics and music also occupied him
on occasion.
It is evident that Gassendi's influence on science
was more philosophical than technical and more critical
than systematic. He rationalized physics by introducing
quantity into it through the measurements he
undertook but above all by introducing atoms, those
mutually combinable units that are capable of joining
together in molecules and of producing measurable
bodies. It is regrettable that with excessive modesty
he refrained from propounding general views of the
sort that can direct and enrich experiment a priori and
that he did not envisage the possibility of applying
mathematics to concrete, physical cases.21
NOTES
1. In Gassendi one sees primarily a precursor of Locke and
Condillac, mentioned later in this article, as well as Hume. See
Tricentenaire de Gassendi, pp. 69, 227.
2. “Avant-propos” to “Mémoire sur
Démocrite et Épicure,” in
Oeuvres, J. Molitor, trans., I (Paris, 1946), xxii.
3. This and the following three paragraphs have been freely
inspired by the excellent thesis of M. Bloch (see below), who
generously lent it to the author.
4. Cf. Libertinage érudit (Paris, 1943), p. 301,
passim.
5. On this point, Bloch rehabilitates Étienne de Clave, a chemist
condemned in 1624 by the Parlement of Paris.
6. Letter, in Le opere di Galileo Galilei, Favaro, ed. (Florence,
1890-1909), V, 309 ff. Gassendi does not approach the position
of “double truth” to the extent that Bloch (see especially his
ch. 11) thinks he does in his desire to reconcile Epicureanism
and literal dogma. He thought he could juxtapose not two
truths but facts equally real although differently expressed.
Misunderstandings taught him what “precautions” (see following