Geoscience Reference
In-Depth Information
14.4.2 The first experimental analyses
Perrault's interpretations
Not much is known about the life of Pierre Perrault (1608-1680). He was born into a
bourgeois family, had at least seven siblings and appears to have spent most of his life in Paris
(see Hallays, 1926; Delorme, 1948; A. Picon in Perrault, 1993). Actually, more is known
about several of his younger brothers: Claude (1613-1688), one of the original members of
the Academie Royale des Sciences, was a physician, a naturalist and an architect; Nicolas
(1623-1661) was a doctor in theology, who was expelled from the Sorbonne around 1655
for his Jansenism and known for his denunciation of the Jesuits; Charles (1628-1703) was
controller of the King's buildings and author of the Mother Goose fairy tales. Like his father
Pierre and his older brother Jean (1610-1669), Pierre Perrault was originally educated for
the legal profession. With this background, he purchased the position of Receiver General
of Finances for Paris. But because of some unexpected changes in the tax arrangements,
around 1664 he came heavily into debt with the royal treasury and was subsequently forced
to give up this post. At this point he was essentially broke and turned to hydrology and
literature. It is unclear exactly why he set out to focus on the origin of springs. Was it a
coincidence that around the same time his brother Claude translated the work of Vitruvius
(Vitruve, 1986)? It should be recalled that Book 8 of that work is devoted to this very topic
and that Pierre classified Vitruvius (correctly) as one of the proponents of the Common
Opinion.
In any event, in the second half of his 1674 topic he starts immediately (p. 148) by
contrasting his own views with the Common Opinion, as quoted in the previous section,
and then (p. 150) he states the two main difficulties with it, as he sees them.
The first is this supposed penetration of the earth by the waters of the rain, which to me does not seem
possible in the manner they mean; the second is that I don't think that enough rain and snow water
falls to soak the earth to the extent necessary, nor that there would still be enough left over to make the
springs and rivers flow, which are produced by it, as they say, and in the manner they assume.
To support these two objections and to shed some light on the matter, Perrault proceeds to
describe a soil water flow experiment he conducted. He took a 65 cm (2 pieds) long lead
pipe with a diameter of 4.5 cm (20 lignes), closed off at the bottom with permeable cloth
and filled with coarse river sand, and he inserted it about 1 cm (4 lignes) into the water
contained in a wide shallow vessel (see Figure 14.4). (The stated dimensions are converted,
here and in what follows, by assuming that 1 French inch or 1 pouce
=
2.707 cm (Petit
Larousse, 1964); also, 1 inch
12 foot.) After 24 h he observed that the water
had risen and moistened the sand up to a level of 49 cm (18 pouces). To verify whether
the risen water could flow out sideways to form springs, he made an opening in the pipe
with a diameter of about 1.8 cm (7-8 lignes) at a height of about 5.4 cm (2 pouces) above
the water surface, where he attached a small 5.4 cm long gutter, sloping down, in which he
placed a strip of paper covered with a thin layer of sand in contact with that of the column.
To his surprise, although the paper and the sand in the gutter became moist, never a single
drop fell from this little gutter. To check further whether any water would ever flow out, he
withdrew the sand column from the water and suspended it for half a day above an empty
tray, but again no water flowed out of all that had earlier risen 49 cm. He then poured some
water on the top of the column to soak the sand, but only three quarters of it came through
at the bottom. The next day, after having poured on again the same amount, all the water
passed through. Finally, the following day, he shook all the sand from the bottom of the
pipe and observed that the soil which came out first was wet like mortar, whereas that which
=
12 lines
=
1
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