LXXIV. Have we attained a knowledge of the cause of the elastic motion,
which is the property that makes a wand or a sword-blade which is
forcibly bent, recover of itself, the straight form it had before, or if
it was naturally bent or crooked, and was opened and made straight by
force, makes it return to its original crooked shape? Descartes, for the
explanation of this phenomenon, recurs to his common asylum, the impulse
of the subtil matter, which not being able to penetrate the pores of the
wand or sword-blade on the hollow side, where the pores are closed by
the inflexion, by its great efforts to open and penetrate them, causes
the wand or sword-blade to recover its former figure. But who does not
perceive, that for this purpose, it will be necessary to suppose the
subtil matter should be for ever moving in opposite directions, from west
to east, and upwards and downwards, &c. for the wand or sword-blade, to
whatever aspect you turn the hollow side, recovers its natural figure
equally the same? Besides, Descartes supposes the subtil matter to be
infinitely fluid, from whence it follows, that it will be impossible to
shut the pores in such a manner, as that they will become impenetrable to
it.
LXXV. Others say, that the same impulse which is impressed on a wand or
bow by him that bends it, is the thing which opens it afterwards. But
against this opinion, it may be urged in the first place, that he who
bends it, does it gradually and by slow degrees; and the impetus with
which it opens, is violent and quick. Secondly, the archer who bends a
bow, is not possessed of a force equal to that, with which it reverts
to its former figure, for that is so great when the arrow is drawn
near the head, that it is capable of giving it an impetus, that will
pierce a substantial thick body through and through; and how can any one
communicate a force or impulse, which is greater than that he possesses?
LXXVI. The Aristotelites, who are great adepts at the easy invention of
giving the name of quality, virtue, or faculty, to express the cause they
are enquiring after, and by the addition of an adjective to that name,
which is a denomination taken from the effect, say, that the cause of
the elastic motion, is an elastic virtue which is inherent in the wand
or sword-blade. This is in reality, having found out a master key, to
unlock all the mysteries of nature; for there is nothing so obscure, that
with this invention may not be made manifest. If you ask, what is the
cause of the marvellous properties of the load-stone, the answer is, the
magnetic virtue; if you ask, what are the causes that perform in us the
operations, of the concoction of aliments, the expulsion of excrements,
and that of nutrition, &c. the answer is, that they are performed by
a concoctive virtue, an expulsive virtue, and a nutritive one; and
according to the same mode of reasoning, the cause of the winds, is a
ventilating virtue, that of lightning a fulminating one, and that of the
flux and reflux of the sea, is owing to two opposite virtues, the one
fluxive, and the other refluxive. By this cheap mode of philosophizing,
every thing is demonstrated at a glance. But to speak seriously, what is
this, but answering in the very language of the question? Saying that
the cause of the elastic motion, is the elastic virtue, is in effect the
same as saying, the cause of the elastic motion, is the cause of the
elastic motion; and saying the magnetic virtue, is that which causes the
load-stone to attract the iron, is answering in the stile of pleasantry,
which some children have studied, and are very ready at; who when a
person asks one of them, _My lad, whose son are you? the boy answers my
father’s_.