Geoscience Reference
In-Depth Information
Fig. 14.6 Sketch in support of
Mariotte's assertion,
that water condensed
inside a mountain
cannot possibly flow
out as a spring.
(From Mariotte,
1686; courtesy
Division of Rare and
Manuscript
Collections, Cornell
University Library.)
as illustrated in Figure 14.6, that if ABC is a vault in a mountain DEF, the water condensed
on this concave surface ABC would fall down to HGI, instead of to L or M, so that it would
be incapable of making a spring; he also rejects that there are many such caves. He counters
the argument of some that there is earth beside or below ABC, by explaining that in this case
the vapors will escape toward A and C, and will yield very little water; moreover, because
there is always clayey soil where there are springs, it is unlikely that these condensed waters
will be able to pass through from the inside of the mountains.
Next, without mentioning them, he deals with those, like Seneca and Perrault, who
claimed that rain cannot penetrate into the soil.
Still others object that the summer rains, although very big, enter the earth only about half a foot,
which one can observe in the gardens & in the tilled fields: I remain in agreement with the experiment.
However, I maintain that in non cultivated soils & in the woods there are some little channels, which
are quite close to the surface, in which rain water enters, & that these channels extend down to great
depths, as one sees in deep dug wells, & that when it rains ten or twelve days in a row, at the end the top
of the tilled soils becomes completely wet, & the remainder of the water passes in the little channels,
which are below & which have not been broken by tillage.
He goes on to illustrate this with his own observations in the cellars of the Royal Observatory
and inside several quarries. In these places water would drip down from the ceiling, but
invariably this water could be seen to issue from small holes, crannies and cracks in the
rocky vault, while the rest of the surface remained dry; also, this dripping was mostly in
response to rain, and would cease during droughts, which suggests that springs are made in
the same way. Among many other examples, he notes that during the dry summer of 1681
many wells and springs dried up, and that after a cold spell in the fall they continued to
decrease; they would not have done this if the water had been formed by vapors raised from
below and condensed by the cold of the surface. Furthermore springs, which are high up
in the mountains, are always adjacent to even higher areas, and their flows are larger when
these areas are larger; again, this indicates that they are produced by the rains which fall on
these higher surfaces.
Finally (p. 30), he addresses the objection by some that the total yearly rain may not be
able to supply enough to the great rivers which flow into the sea. He resolves the problem,
like Perrault, by comparing river flow with the rainfall on the upstream watershed area;
however, his watershed area is much larger and his estimation of the river discharge is
also much more rigorous. From measurements over an eight-year period, he estimates the
rainfall at Dijon to be about 46 cm (17 pouces), adding that a similar measurement by
the “author of the topic entitled 'On the Origin of Springs”' yielded a value of 51.96 cm
(19 pouces, 2.33 lignes); but for the purpose of the exercise he decides to adopt a conservative
