but merely to their composition, as whether they easily incorporate
with each other, or there be rather (as an example) certain winds and
exhalations, or other spiritual bodies, which do not mix with common
air, but only adhere to and float in it in globules and drops, and
are rather broken and pounded by the air, than received into, and
incorporated with it; this cannot be perceived in common air, and other
aëriform substances, on account of the rarity of the bodies, but an
image, as it were, of this process may be conceived in such liquids
as quicksilver, oil, water, and even air, when broken and dissipated
it ascends in small portions through water, and also in the thicker
kinds of smoke; lastly, in dust, raised and remaining in the air, in
all of which there is no incorporation: and the above representation
in this respect is not a bad one, if it be first diligently
investigated, whether there can be such a difference of nature between
spirituous substances, as between liquids, for then these images might
conveniently be substituted by analogy.
And although we have observed of these supplementary instances, that
information is to be derived from them, when appropriate instances are
wanting, by way of refuge, yet we would have it understood, that they
are also of great use, when the appropriate instances are at hand, in
order to confirm the information afforded by them; of which we will
speak more at length, when our subject leads us, in due course, to the
support of induction.
XLIII. In the twentieth rank of prerogative instances we will place
lancing instances, which we are also wont (but for a different reason)
to call twitching instances. We adopt the latter name, because they
twitch the understanding, and the former because they pierce nature,
whence we style them occasionally the instances of Democritus.[143]
They are such as warn the understanding of the admirable and
exquisite subtilty of nature, so that it becomes roused and awakened
to attention, observation, and proper inquiry; as, for instance,
that a little drop of ink should be drawn out into so many letters;
that silver merely gilt on its surface should be stretched to such a
length of gilt wire; that a little worm, such as you may find on the
skin, should possess both a spirit and a varied conformation of its
parts; that a little saffron should imbue a whole tub of water with
its color; that a little musk or aroma should imbue a much greater
extent of air with its perfume; that a cloud of smoke should be
raised by a little incense; that such accurate differences of sounds
as articulate words should be conveyed in all directions through the
air, and even penetrate the pores of wood and water (though they
become much weakened), that they should be, moreover, reflected, and
that with such distinctness and velocity; that light and color should
for such an extent and so rapidly pass through solid bodies, such as
glass and water, with so great and so exquisite a variety of images,
and should be refracted and reflected; that the magnet should attract
through every description of body, even the most compact; but (what
is still more wonderful) that in all these cases the action of one
should not impede that of another in a common medium, such as air;
and that there should be borne through the air, at the same time, so
many images of visible objects, so many impulses of articulation, so
many different perfumes, as of the violet, rose, etc., besides cold and
heat, and magnetic attractions; all of them, I say, at once, without
any impediment from each other, as if each had its paths and peculiar
passage set apart for it, without infringing against or meeting each
other.
To these lancing instances, however, we are wont, not without some
advantage, to add those which we call the limits of such instances.
Thus, in the cases we have pointed out, one action does not disturb or
impede another of a different nature, yet those of a similar nature
subdue and extinguish each other; as the light of the sun does that of
the candle, the sound of a cannon that of the voice, a strong perfume a
more delicate one, a powerful heat a more gentle one, a plate of iron
between the magnet and other iron the effect of the magnet. But the
proper place for mentioning these will be also among the supports of
induction.
XLIV. We have now spoken of the instances which assist the senses,
and which are principally of service as regards information; for
information begins from the senses. But our whole labor terminates in
practice, and as the former is the beginning, so is the latter the
end of our subject. The following instances, therefore, will be those
which are chiefly useful in practice. They are comprehended in two
classes, and are seven in number. We call them all by the general name
of practical instances. Now there are two defects in practice, and as
many divisions of important instances. Practice is either deceptive or
too laborious. It is generally deceptive (especially after a diligent
examination of natures), on account of the power and actions of
bodies being ill defined and determined. Now the powers and actions
of bodies are defined and determined either by space or by time, or
by the quantity at a given period, or by the predominance of energy;
and if these four circumstances be not well and diligently considered,
the sciences may indeed be beautiful in theory, but are of no effect
in practice. We call the four instances referred to this class,
mathematical instances and instances of measure.
Practice is laborious either from the multitude of instruments, or
the bulk of matter and substances requisite for any given work. Those
instances, therefore, are valuable, which either direct practice to
that which is of most consequence to mankind, or lessen the number of
instruments or of matter to be worked upon. We assign to the three
instances relating to this class, the common name of propitious or
benevolent instances. We will now separately discuss these seven
instances, and conclude with them that part of our work which relates
to the prerogative or illustrious instances.
XLV. In the twenty-first rank of prerogative instances we will place
the instances of the rod or rule, which we are also wont to call the
instances of completion or _non ultrà_. For the powers and motions of
bodies do not act and take effect through indefinite and accidental,
but through limited and certain spaces; and it is of great importance
to practice that these should be understood and noted in every nature
which is investigated, not only to prevent deception, but to render
practice more extensive and efficient. For it is sometimes possible to
extend these powers, and bring the distance, as it were, nearer, as in
the example of telescopes.
Many powers act and take effect only by actual touch, as in the
percussion of bodies, where the one does not remove the other, unless
the impelling touch the impelled body. External applications in
medicine, as ointment and plasters, do not exercise their efficacy
except when in contact with the body. Lastly, the objects of touch and
taste only strike those senses when in contact with their organs.
Other powers act at a distance, though it be very small, of which but
few have as yet been noted, although there be more than men suspect;
this happens (to take everyday instances) when amber or jet attracts
straws, bubbles dissolve bubbles, some purgative medicines draw humors
from above, and the like. The magnetic power by which iron and the
magnet, or two magnets, are attracted together, acts within a definite
and narrow sphere, but if there be any magnetic power emanating from
the earth a little below its surface, and affecting the needle in its
polarity, it must act at a great distance.
Again, if there be any magnetic force which acts by sympathy between
the globe of the earth and heavy bodies, or between that of the moon
and the waters of the sea (as seems most probable from the particular
floods and ebbs which occur twice in the month), or between the starry
sphere and the planets, by which they are summoned and raised to their
apogees, these must all operate at very great distances.[144]
Again, some conflagrations and the kindling of flames take place
at very considerable distances with particular substances, as they
report of the naphtha of Babylon. Heat, too, insinuates itself at wide
distances, as does also cold, so that the masses of ice which are
broken off and float upon the Northern Ocean, and are borne through the
Atlantic to the coast of Canada, become perceptible by the inhabitants,
and strike them with cold from a distance. Perfumes also (though here
there appears to be always some corporeal emission) act at remarkable
distances, as is experienced by persons sailing by the coast of
Florida, or parts of Spain, where there are whole woods of lemons,
oranges, and other odoriferous plants, or rosemary and marjoram bushes,
and the like. Lastly, the rays of light and the impressions of sound
act at extensive distances.
Yet all these powers, whether acting at a small or great distance,
certainly act within definite distances, which are well ascertained
by nature, so that there is a limit depending either on the mass or
quantity of the bodies, the vigor or faintness of the powers, or the
favorable or impeding nature of the medium, all of which should be
taken into account and observed. We must also note the boundaries of
violent motions, such as missiles, projectiles, wheels and the like,
since they are also manifestly confined to certain limits.
Some motions and virtues are to be found of a directly contrary nature
to these, which act in contact but not at a distance; namely, such as
operate at a distance and not in contact, and again act with less force
at a less distance, and the reverse. Sight, for instance, is not easily
effective in contact, but requires a medium and distance; although I
remember having heard from a person deserving of credit, that in being
cured of a cataract (which was done by putting a small silver needle
within the first coat of the eye, to remove the thin pellicle of the
cataract, and force it into a corner of the eye), he had distinctly
seen the needle moving across the pupil. Still, though this may be
true, it is clear that large bodies cannot be seen well or distinctly,
unless at the vertex of a cone, where the rays from the object meet
at some distance from the eye. In old persons the eye sees better if
the object be moved a little further, and not nearer. Again, it is
certain that in projectiles the impact is not so violent at too short
a distance as a little afterward.[145] Such are the observations to be
made on the measure of motions as regards distance.
There is another measure of motion in space which must not be passed
over, not relating to progressive but spherical motion--that is,
the expansion of bodies into a greater, or their contraction into a
lesser sphere. For in our measure of this motion we must inquire what
degree of compression or extension bodies easily and readily admit of,
according to their nature, and at what point they begin to resist it,
so as at last to bear it no further--as when an inflated bladder is
compressed, it allows a certain compression of the air, but if this be
increased, the air does not suffer it, and the bladder is burst.
We have proved this by a more delicate experiment. We took a metal
bell, of a light and thin sort, such as is used for salt-cellars, and
immersed it in a basin of water, so as to carry the air contained in
its interior down with it to the bottom of the basin. We had first,
however, placed a small globe at the bottom of the basin, over which
we placed the bell. The result was, that if the globe were small
compared with the interior of the bell, the air would contract itself,
and be compressed without being forced out, but if it were too large
for the air readily to yield to it, the latter became impatient of the
pressure, raised the bell partly up, and ascended in bubbles.
To prove, also, the extension (as well as the compression) which air
admits of, we adopted the following method:--We took a glass egg, with
a small hole at one end; we drew out the air by violent suction at
this hole, and then closed the hole with the finger, immersed the egg
in water, and then removed the finger. The air being constrained by
the effort made in suction, and dilated beyond its natural state, and
therefore striving to recover and contract itself (so that if the egg
had not been immersed in water, it would have drawn in the air with a
hissing sound), now drew in a sufficient quantity of water to allow
the air to recover its former dimensions.[146]
It is well ascertained that rare bodies (such as air) admit of
considerable contraction, as has been before observed; but tangible
bodies (such as water) admit of it much less readily, and to a less
extent. We investigated the latter point by the following experiment:
We had a leaden globe made, capable of containing about two pints, wine
measure, and of tolerable thickness, so as to support considerable
pressure. We poured water into it through an aperture, which we
afterward closed with melted lead, as soon as the globe was filled with
water, so that the whole became perfectly solid. We next flattened the
two opposite sides with a heavy hammer, which necessarily caused the
water to occupy a less space, since the sphere is the solid of greatest
content; and when hammering failed from the resistance of the water,
we made use of a mill or press, till at last the water, refusing to
submit to a greater pressure, exuded like a fine dew through the solid
lead. We then computed the extent to which the original space had been
reduced, and concluded that water admitted such a degree of compression
when constrained by great violence.
The more solid, dry or compact bodies, such as stones, wood and metals,
admit of much less, and indeed scarcely any perceptible compression or
expansion, but escape by breaking, slipping forward, or other efforts;
as appears in bending wood, or steel for watch-springs, in projectiles,
hammering and many other motions, all of which, together with their
degrees, are to be observed and examined in the investigation of
nature, either to a certainty, or by estimation, or comparison, as
opportunity permits.
XLVI. In the twenty-second rank of prerogative instances we will
place the instances of the course, which we are also wont to call
water instances, borrowing our expression from the water hour-glasses
employed by the ancients instead of those with sand. They are such as
measure nature by the moments of time, as the last instances do by the
degrees of space. For all motion or natural action takes place in time,
more or less rapidly, but still in determined moments well ascertained
by nature. Even those actions which appear to take effect suddenly, and
in the twinkling of an eye (as we express it), are found to admit of
greater or less rapidity.
In the first place, then, we see that the return of the heavenly bodies
to the same place takes place in regular times, as does the flood and
ebb of the sea. The descent of heavy bodies toward the earth, and
the ascent of light bodies toward the heavenly sphere, take place in
definite times,[147] according to the nature of the body, and of the
medium through which it moves. The sailing of ships, the motions of
animals, the transmission of projectiles, all take place in times
the sums of which can be computed. With regard to heat, we see that
boys in winter bathe their hands in the flame without being burned;
and conjurers, by quick and regular movements, overturn vessels filled
with wine or water, and replace them without spilling the liquid, with
several similar instances. The compression, expansion and eruption
of several bodies, take place more or less rapidly, according to the
nature of the body and its motion, but still in definite moments.
In the explosion of several cannon at once (which are sometimes heard
at the distance of thirty miles), the sound of those nearest to the
spot is heard before that of the most distant. Even in sight (whose
action is most rapid), it is clear that a definite time is necessary
for its exertion, which is proved by certain objects being invisible
from the velocity of their motion, such as a musket-ball; for the
flight of the ball is too swift to allow an impression of its figure to
be conveyed to the sight.
This last instance, and others of a like nature, have sometimes excited
in us a most marvellous doubt, no less than whether the image of the
sky and stars is perceived as at the actual moment of its existence,
or rather a little after, and whether there is not (with regard to the
visible appearance of the heavenly bodies) a true and apparent time,
as well as a true and apparent place, which is observed by astronomers
in parallaxes. It appeared so incredible to us, that the images or
radiations of heavenly bodies could suddenly be conveyed through such
immense spaces to the sight, and it seemed that they ought rather to be
transmitted in a definite time.[148] That doubt, however (as far as
regards any great difference between the true and apparent time), was
subsequently completely set at rest, when we considered the infinite
loss and diminution of size as regards the real and apparent magnitude
of a star, occasioned by its distance, and at the same time observed
at how great a distance (at least sixty miles) bodies which are merely
white can be suddenly seen by us. For there is no doubt, that the light
of the heavenly bodies not only far surpasses the vivid appearance of
white, but even the light of any flame (with which we are acquainted)
in the vigor of its radiation. The immense velocity of the bodies
themselves, which is perceived in their diurnal motion, and has so
astonished thinking men, that they have been more ready to believe in
the motion of the earth, renders the motion of radiation from them
(marvellous as it is in its rapidity) more worthy of belief. That
which has weighed most with us, however, is, that if there were any
considerable interval of time between the reality and the appearance,
the images would often be interrupted and confused by clouds formed in
the meantime, and similar disturbances of the medium. Let this suffice
with regard to the simple measures of time.
It is not merely the absolute, but still more the relative measure of
motions and actions which must be inquired into, for this latter is
of great use and application. We perceive that the flame of firearms
is seen sooner than the sound is heard, although the ball must have
struck the air before the flame, which was behind it, could escape:
the reason of which is, that light moves with greater velocity than
sound. We perceive, also, that visible images are received by the sight
with greater rapidity than they are dismissed, and for this reason, a
violin string touched with the finger appears double or triple, because
the new image is received before the former one is dismissed. Hence,
also, rings when spinning appear globular, and a lighted torch, borne
rapidly along at night, appears to have a tail. Upon the principle of
the inequality of motion, also, Galileo attempted an explanation of
the flood and ebb of the sea, supposing the earth to move rapidly, and
the water slowly, by which means the water, after accumulating, would
at intervals fall back, as is shown in a vessel of water made to move
rapidly. He has, however, imagined this on data which cannot be granted
(namely, the earth’s motion), and besides, does not satisfactorily
account for the tide taking place every six hours.
An example of our present point (the relative measure of motion), and,
at the same time, of its remarkable use of which we have spoken, is
conspicuous in mines filled with gunpowder, where immense weights of
earth, buildings, and the like, are overthrown and prostrated by a
small quantity of powder; the reason of which is decidedly this, that
the motion of the expansion of the gunpowder is much more rapid than
that of gravity,[149] which would resist it, so that the former has
terminated before the latter has commenced. Hence, also, in missiles,
a strong blow will not carry them so far as a sharp and rapid one.
Nor could a small portion of animal spirit in animals, especially in
such vast bodies as those of the whale and elephant, have ever bent or
directed such a mass of body, were it not owing to the velocity of the
former, and the slowness of the latter in resisting its motion.
In short, this point is one of the principal foundations of the magic
experiments (of which we shall presently speak), where a small mass
of matter overcomes and regulates a much larger, if there but be an
anticipation of motion, by the velocity of one before the other is
prepared to act.
Finally, the point of the first and last should be observed in all
natural actions. Thus, in an infusion of rhubarb the purgative property
is first extracted, and then the astringent; we have experienced
something of the same kind in steeping violets in vinegar, which first
extracts the sweet and delicate odor of the flower, and then the
more earthy part, which disturbs the perfume; so that if the violets
be steeped a whole day, a much fainter perfume is extracted than if
they were steeped for a quarter of an hour only, and then taken out;
and since the odoriferous spirit in the violet is not abundant, let
other and fresh violets be steeped in the vinegar every quarter of an
hour, as many as six times, when the infusion becomes so strengthened,
that although the violets have not altogether remained there for more
than one hour and a half, there remains a most pleasing perfume, not
inferior to the flower itself, for a whole year. It must be observed,
however, that the perfume does not acquire its full strength till
about a month after the infusion. In the distillation of aromatic
plants macerated in spirits of wine, it is well known that an aqueous
and useless phlegm rises first, then water containing more of the
spirit, and, lastly, water containing more of the aroma; and many
observations of the like kind, well worthy of notice, are to be made in
distillations. But let these suffice as examples.[150]
XLVII. In the twenty-third rank of prerogative instances we will place
instances of quantity, which we are also wont to call the doses of
nature (borrowing a word from medicine). They are such as measure the
powers by the quantity of bodies, and point out the effect of the
quantity in the degree of power. And in the first place, some powers
only subsist in the universal quantity, or such as bears a relation to
the confirmation and fabric of the universe. Thus the earth is fixed,
its parts fall. The waters in the sea flow and ebb, but not in the
rivers, except by the admission of the sea. Then, again, almost all
particular powers act according to the greater or less quantity of the
body. Large masses of water are not easily rendered foul, small are.
New wine and beer become ripe and drinkable in small skins much more
readily than in large casks. If a herb be placed in a considerable
quantity of liquid, infusion takes place rather than impregnation;
if in less, the reverse. A bath, therefore, and a light sprinkling,
produce different effects on the human body. Light dew, again, never
falls, but is dissipated and incorporated with the air; thus we see
that in breathing on gems, the slight quantity of moisture, like a
small cloud in the air, is immediately dissolved. Again, a piece of
the same magnet does not attract so much iron as the whole magnet did.
There are some powers where the smallness of the quantity is of more
avail; as in boring, a sharp point pierces more readily than a blunt
one; the diamond, when pointed, makes an impression on glass, and the
like.
Here, too, we must not rest contented with a vague result, but inquire
into the exact proportion of quantity requisite for a particular
exertion of power; for one would be apt to suppose that the power bears
an exact proportion to the quantity; that if a leaden bullet of one
ounce, for instance, would fall in a given time, one of two ounces
ought to fall twice as rapidly, which is most erroneous. Nor does the
same ratio prevail in every kind of power, their difference being
considerable. The measure, therefore, must be determined by experiment,
and not by probability or conjecture.
Lastly, we must in all our investigations of nature observe what
quantity, or dose, of the body is requisite for a given effect, and
must at the same time be guarded against estimating it at too much or
too little.