terranean courses of water, like those which are made between
the air and the earth, are those which continually consume and deepen
the beds of their currents. The earth which is carried by rivers is
discharged at the end of their course, that is to say, the earth
carried from the highest part of the river's course is discharged at
the lowest depth of its course. Where fresh water arises in the sea,
the miracle of the creation of an island is manifest, which will be
discovered sooner or later in proportion as the quantity of water is
greater or less. And an island of this kind is formed by the deposit
of earth and stones made by the subterranean current of water in the
channels through which it passes.

{168}

[Sidenote: Nature's Law]

65.

Nature never breaks her laws.

66.

Nature is constrained by the cause of her laws which dwells inborn in
her.

67.

Without reason no effect is produced in nature; understand the reason
and you will not need experience.

[Sidenote: Cause discovered by Effect]

68.

Before I proceed further I will make some experiments, because it is my
intention to cite the experiment first and then to demonstrate by
reasoning how such an experiment must necessarily take effect in such a
manner. And this is the true rule by which investigations of natural
phenomena must proceed; and although nature herself begins from the
reason and ends in the result, we must pursue the contrary course and
begin, as I said above, from experience and by it seek out the reason.

[Sidenote: Repetition of Experiment]

69.

Before deducing a general rule from this case repeat the experiment two
or three times and see if the same results are produced.

{169}

[Sidenote: Example of preceding Rule]

70.

It several bodies of equal weight and shape are dropped one after
another at equal intervals of time, the distances between each
successive body will be equally increased.

The experiment to prove the above-mentioned theorem respecting motion
must be made thus: Take two balls of equal weight and shape and let
them fall from a great height so that when they start falling they
touch one another, and let the investigator stand on the ground and
watch whether the contact is maintained during their fall. This
experiment must be repeated several times, so that the trial may not be
marred by any accident and the experiment vitiated and the spectator
deceived.

[Sidenote: Necessity o