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Some coruscations emit light without burning, but are never accompanied
by thunder.

Eructations and eruptions of flame are to be found in cold climates
as well as in hot, as in Iceland and Greenland; just as the trees of
cold countries are sometimes inflammable and more pitchy and resinous
than in warm, as the fir, pine, and the like. But the position and
nature of the soil, where such eruptions are wont to happen, is not yet
sufficiently investigated to enable us to subjoin a negative instance
to the affirmative.

All flame is constantly more or less warm, and this instance is not
altogether negative; yet it is said that the ignis fatuus (as it is
called), and which sometimes is driven against walls, has but little
heat; perhaps it resembles that of spirits of wine, which is mild and
gentle. That flame, however, appears yet milder, which in some well
authenticated and serious histories is said to have appeared round the
head and hair of boys and virgins, and instead of burning their hair,
merely to have played about it. And it is most certain that a sort of
flash, without any evident heat, has sometimes been seen about a horse
when sweating at night, or in damp weather. It is also a well known
fact,[89] and it was almost considered as a miracle, that a few years
since a girl’s apron sparkled when a little shaken or rubbed, which
was, perhaps, occasioned by the alum or salts with which the apron
was imbued, and which, after having been stuck together and incrusted
rather strongly, were broken by the friction. It is well known that
all sugar, whether candied or plain, if it be hard, will sparkle when
broken or scraped in the dark. In like manner sea and salt water is
sometimes found to shine at night when struck violently by the oar. The
foam of the sea when agitated by tempests also sparkles at night, and
the Spaniards call this appearance the sea’s lungs. It has not been
sufficiently ascertained what degree of heat attends the flame which
the ancient sailors called Castor and Pollux, and the moderns call
St. Ermus’ fire.

Every ignited body that is red-hot is always warm, although without
flame, nor is any negative instance subjoined to this affirmative.
Rotten wood, however, approaches nearly to it, for it shines at night,
and yet is not found to be warm; and the putrefying scales of fish
which shine in the same manner are not warm to the touch, nor the body
of the glowworm, or of the fly called Lucciola. [90]

The situation and nature of the soil of natural warm baths has not been
sufficiently investigated, and therefore a negative instance is not
subjoined.

To the instances of warm liquids we may subjoin the negative one of the
peculiar nature of liquids in general; for no tangible liquid is known
that is at once warm in its nature and constantly continues warm; but
their heat is only superinduced as an adventitious nature for a limited
time, so that those which are extremely warm in their power and effect,
as spirits of wine, chemical aromatic oils, the oils of vitriol and
sulphur, and the like, and which speedily burn, are yet cold at first
to the touch, and the water of natural baths, poured into any vessel
and separated from its source, cools down like water heated by the
fire. It is, however, true that oily substances are rather less cold
to the touch than those that are aqueous, oil for instance than water,
silk than linen; but this belongs to the table of degrees of cold.

In like manner we may subjoin a negative instance to that of warm
vapor, derived from the nature of vapor itself, as far as we are
acquainted with it. For exhalations from oily substances, though easily
inflammable, are yet never warm unless recently exhaled from some warm
substance.

The same may be said of the instance of air; for we never perceive that
air is warm unless confined or pressed, or manifestly heated by the
sun, by fire, or some other warm body.

A negative instance is exhibited in weather by its coldness with an
east or north wind, beyond what the season would lead us to expect,
just as the contrary takes place with the south or west winds. An
inclination to rain (especially in winter) attends warm weather, and to
frost cold weather.

A negative instance as to air confined in caverns may be observed in
summer. Indeed, we should make a more diligent inquiry into the nature
of confined air. For in the first place the qualities of air in its own
nature with regard to heat and cold may reasonably be the subject of
doubt; for air evidently derives its heat from the effects of celestial
bodies, and possibly its cold from the exhalation of the earth, and
in the mid region of air (as it is termed) from cold vapors and snow,
so that no judgment can be formed of the nature of air by that which
is out of doors and exposed, but a more correct one might be derived
from confined air. It is necessary, however, that the air should be
inclosed in a vessel of such materials as would not imbue it with heat
or cold of themselves, nor easily admit the influence of the external
atmosphere. The experiment should be made, therefore, with an earthen
jar, covered with folds of leather to protect it from the external
air, and the air should be kept three or four days in this vessel well
closed. On opening the jar, the degree of heat may be ascertained
either by the hand or a graduated glass tube.

There is a similar doubt as to whether the warmth of wool, skins,
feathers, and the like, is derived from a slight inherent heat, since
they are animal excretions, or from their being of a certain fat and
oily nature that accords with heat, or merely from the confinement and
separation of air which we spoke of in the preceding paragraph;[91] for
all air appears to possess a certain degree of warmth when separated
from the external atmosphere. Let an experiment be made, therefore,
with fibrous substances of linen, and not of wool, feathers, or silk,
which are animal excretions. For it is to be observed that all powders
(where air is manifestly inclosed) are less cold than the substances
when whole, just as we imagine froth (which contains air) to be less
cold than the liquid itself.

We have here no exactly negative instance, for we are not acquainted
with any body tangible or spirituous which does not admit of heat when
exposed to the fire. There is, however, this difference, that some
admit it more rapidly, as air, oil, and water, others more slowly, as
stone and metals. [92] This, however, belongs to the table of degrees.

No negative is here subjoined, except the remark that sparks are not
kindled by flint and steel, or any other hard substance, unless some
small particles of the stone or metal are struck off, and that the air
never forms them by friction, as is commonly supposed; besides, the
sparks from the weight of the ignited substance have a tendency to
descend rather than to rise, and when extinguished become a sort of
dark ash.

We are of opinion that here again there is no negative; for we are not
acquainted with any tangible body which does not become decidedly warm
by friction, so that the ancients feigned that the gods had no other
means or power of creating heat than the friction of air, by rapid
and violent rotation. On this point, however, further inquiry must be
made, whether bodies projected by machines (as balls from cannon) do
not derive some degree of heat from meeting the air, which renders
them somewhat warm when they fall. The air in motion rather cools
than heats, as in the winds, the bellows, or breath when the mouth is
contracted. The motion, however, in such instances is not sufficiently
rapid to excite heat, and is applied to a body of air, and not to its
component parts, so that it is not surprising that heat should not be
generated.

We must make a more diligent inquiry into this instance; for herbs and
green and moist vegetables appear to possess a latent heat, so small,
however, as not to be perceived by the touch in single specimens, but
when they are united and confined, so that their spirit cannot exhale
into the air, and they rather warm each other, their heat is at once
manifested, and even flame occasionally in suitable substances.

Here, too, we must make a more diligent inquiry; for quicklime, when
sprinkled with water, appears to conceive heat, either from its being
collected into one point (as we observed of herbs when confined), or
from the irritation and exasperation of the fiery spirit by water,
which occasions a conflict and struggle. The true reason will more
readily be shown if oil be used instead of water, for oil will
equally tend to collect the confined spirit, but not to irritate.
The experiment may be made more general, both by using the ashes and
calcined products of different bodies and by pouring different liquids
upon them.

A negative instance may be subjoined of other metals which are more
soft and soluble; for leaf gold dissolved by aqua regia, or lead by
aqua fortis, are not warm to the touch while dissolving, no more is
quicksilver (as far as I remember), but silver excites a slight heat,
and so does copper, and tin yet more plainly, and most of all iron and
steel, which excite not only a powerful heat, but a violent bubbling.
The heat, therefore, appears to be occasioned by the struggle which
takes place when these strong dissolvents penetrate, dig into, and tear
asunder the parts of those substances, while the substances themselves
resist. When, however, the substances yield more easily, scarcely any
heat is excited.

There is no negative instance with regard to the heat of animals,
except in insects (as has been observed), owing to their small size;
for in fishes, as compared with land animals, a lower degree rather
than a deprivation of heat is observable. In plants and vegetables,
both as to their exudations and pith when freshly exposed, there is no
sensible degree of heat. But in animals there is a great difference
in the degree, both in particular parts (for the heat varies near the
heart, the brain, and the extremities) and in the circumstances in
which they are placed, such as violent exercise and fevers.

Here, again, there is scarcely a negative instance. I might add that
the excrements of animals, even when they are no longer fresh, possess
evidently some effective heat, as is shown by their enriching the soil.

Such liquids (whether oily or watery) as are intensely acrid exhibit
the effects of heat, by the separation and burning of bodies after
some little action upon them, yet they are not at first warm to the
touch, but they act according to their affinity and the pores of the
substances to which they are applied; for aqua regia dissolves gold but
not silver--on the contrary, aqua fortis dissolves silver but not gold;
neither of them dissolves glass, and so of the rest.

Let spirits of wine be tried on wood, or butter, wax, or pitch, to see
if this will melt them at all by their heat; for the twenty-fourth
instance shows that they possess properties resembling those of heat in
causing incrustation. Let an experiment also be made with a graduated
glass or calendar,[93] concave at the top, by pouring well-rectified
spirits of wine into the cavity, and covering it up in order that they
may the better retain their heat, then observe whether their heat make
the water descend.

Spices and acrid herbs are sensibly warm to the palate, and still
more so when taken internally; one should see, therefore, on what
other substances they exhibit the effects of heat. Now, sailors tell
us that when large quantities of spices are suddenly opened, after
having been shut up for some time, there is some danger of fever and
inflammation to those who stir them or take them out. An experiment
might, therefore, be made whether such spices and herbs, when produced,
will, like smoke, dry fish and meat hung up over them.

There is an acrid effect and a degree of penetration in cold liquids,
such as vinegar and oil of vitriol, as well as in warm, such as oil of
marjoram and the like; they have, therefore, an equal effect in causing
animated substances to smart, and separating and consuming inanimate
parts. There is not any negative instance as to this, nor does there
exist any animal pain unaccompanied by the sensation of heat.

There are many effects common to cold and heat, however different
in their process; for snowballs appear to burn boys’ hands after
a little time, and cold no less than fire preserves bodies from
putrefaction--besides both heat and cold contract bodies. But it is
better to refer these instances and the like to the investigation of
cold.

XIII. In the third place we must exhibit to the understanding the
instances in which that nature, which is the object of our inquiries,
is present in a greater or less degree, either by comparing its
increase and decrease in the same object, or its degree in different
objects; for since the form of a thing is its very essence, and the
thing only differs from its form as the apparent from the actual
object, or the exterior from the interior, or that which is considered
with relation to man from that which is considered with relation to the
universe; it necessarily follows that no nature can be considered a
real form which does not uniformly diminish and increase with the given
nature. We are wont to call this our Table of Degrees, or Comparative
Instances.

_Table of the Degrees or Comparative Instances of Heat_

We will first speak of those bodies which exhibit no degree of heat
sensible to the touch, but appear rather to possess a potential heat,
or disposition and preparation for it. We will then go on to others,
which are actually warm to the touch, and observe the strength and
degree of it.

1. There is no known solid or tangible body which is by its own nature
originally warm; for neither stone, metal, sulphur, fossils, wood,
water, nor dead animal carcasses are found warm. The warm springs in
baths appear to be heated accidentally, by flame, subterraneous fire
(such as is thrown up by Etna and many other mountains), or by the
contact of certain bodies, as heat is exhibited in the dissolution of
iron and tin. The degree of heat, therefore, in inanimate objects is
not sensible to our touch; but they differ in their degrees of cold,
for wood and metal are not equally cold. [94] This, however, belongs to
the Table of Degrees of Cold.

2. But with regard to potential heat and predisposition to flame, we
find many inanimate substances wonderfully adapted to it, as sulphur,
naphtha, and saltpetre.

3. Bodies which have previously acquired heat, as horse dung from the
animal, or lime, and perhaps ashes and soot from fire, retain some
latent portion of it. Hence distillations and separations of substances
are effected by burying them in horse dung, and heat is excited in
lime by sprinkling it with water (as has been before observed).

4. In the vegetable world we know of no plant, nor part of any plant
(as the exudations or pith) that is warm to man’s touch. Yet (as we
have before observed) green weeds grow warm when confined, and some
vegetables are warm and others cold to our internal touch, _i. e. _, the
palate and stomach, or even after a while to our external skin (as is
shown in plasters and ointments).

5. We know of nothing in the various parts of animals, when dead or
detached from the rest, that is warm to the touch; for horse dung
itself does not retain its heat, unless it be confined and buried. All
dung, however, appears to possess a potential heat, as in manuring
fields; so also dead bodies are endued with this latent and potential
heat to such a degree, that in cemeteries where people are interred
daily the earth acquires a secret heat, which consumes any recently
deposited body much sooner than pure earth; and they tell you that the
people of the East are acquainted with a fine soft cloth, made of the
down of birds, which can melt butter wrapped gently up in it by its own
warmth.

6. Manures, such as every kind of dung, chalk, sea-sand, salt and the
like, have some disposition toward heat.

7. All putrefaction exhibits some slight degree of heat, though not
enough to be perceptible by the touch; for neither the substances which
by putrefaction are converted into animalculæ,[95] as flesh and cheese,
nor rotten wood which shines in the dark, are warm to the touch. The
heat, however, of putrid substances displays itself occasionally in a
disgusting and strong scent.

8. The first degree of heat, therefore, in substances which are warm
to the human touch appears to be that of animals, and this admits of a
great variety of degrees, for the lowest (as in insects) is scarcely
perceptible, the highest scarcely equals that of the sun’s rays in
warm climates and weather, and is not so acute as to be insufferable
to the hand. It is said, however, of Constantius, and some others of
a very dry constitution and habit of body, that when attacked with
violent fevers, they became so warm as to appear almost to burn the
hand applied to them.

9. Animals become more warm by motion and exercise, wine and feasting,
venery, burning fevers, and grief.

10. In the paroxysm of intermittent fevers the patients are at first
seized with cold and shivering, but soon afterward become more heated
than at first--in burning and pestilential fevers they are hot from the
beginning.

11. Let further inquiry be made into the comparative heat of different
animals, as fishes, quadrupeds, serpents, birds, and also of the
different species, as the lion, the kite, or man; for, according to the
vulgar opinion, fishes are the least warm internally, and birds the
most, particularly doves, hawks, and ostriches.

12. Let further inquiry be made as to the comparative heat in different
parts and limbs of the same animal; for milk, blood, seed, and eggs are
moderately warm, and less hot than the outward flesh of the animal when
in motion or agitated. The degree of heat of the brain, stomach, heart,
and the rest, has not yet been equally well investigated.

13. All animals are externally cold in winter and cold weather, but are
thought to be internally warmer.

14. The heat of the heavenly bodies, even in the warmest climates and
seasons, never reaches such a pitch as to light or burn the driest wood
or straw, or even tinder without the aid of burning-glasses. It can,
however, raise vapor from moist substances.

15. Astronomers tell us that some stars are hotter than others. Mars
is considered the warmest after the Sun, then Jupiter, then Venus. The
Moon and, above all, Saturn, are considered to be cold. Among the fixed
stars Sirius is thought the warmest, then Cor Leonis or Regulus, then
the lesser Dog-star.

16. The sun gives out more heat as it approaches toward the
perpendicular or zenith, which may be supposed to be the case with the
other planets, according to their degree of heat; for instance, that
Jupiter gives out more heat when situated beneath Cancer or Leo than
when he is beneath Capricorn and Aquarius.

17. It is to be supposed that the sun and other planets give more
heat in perigee, from their approximation to the earth, than when in
apogee. But if in any country the sun should be both in its perigee
and nearer to the perpendicular at the same time, it must necessarily
give out more heat than in a country where it is also in perigee,
but situated more obliquely; so that the comparative altitude of the
planets should be observed, and their approach to or declination from
the perpendicular in different countries.

18. The sun and other planets are thought also to give out more heat in
proportion as they are nearer to the larger fixed stars, as when the
sun is in Leo he is nearer Cor Leonis, Cauda Leonis, Spica Virginis,
Sirius, and the lesser Dog-star, than when he is in Cancer, where,
however, he approaches nearer to the perpendicular. It is probable,
also, that the quarters of the heavens produce a greater heat (though
not perceptibly), in proportion as they are adorned with a greater
number of stars, particularly those of the first magnitude.

19. On the whole, the heat of the heavenly bodies is augmented in three
ways: 1. The approach to the perpendicular; 2. Proximity or their
perigee; 3. The conjunction or union of stars.

20. There is a very considerable difference between the degree of heat
in animals, and even in the rays of the heavenly bodies (as they reach
us), and the heat of the most gentle flame, and even of all ignited
substances, nay, liquids, or the air itself when unusually heated by
fire. For the flame of spirit of wine, though diffused and uncollected,
is yet able to set straw, linen, or paper on fire, which animal heat,
or that of the sun, will never accomplish without a burning-glass.

21. There are, however, many degrees of strength and weakness in flame
and ignited bodies: but no diligent inquiry has been made in this
respect, and we must, therefore, pass it hastily over. Of all flames,
that of spirits of wine appears to be the most gentle, except perhaps
the ignis fatuus, or the flashes from the perspiration of animals.
After this we should be inclined to place the flame of light and porous
vegetables, such as straw, reeds, and dried leaves; from which the
flame of hair or feathers differs but little. Then, perhaps, comes
the flame of wood, particularly that which contains but little rosin
or pitch; that of small wood, however (such as is usually tied up in
fagots), is milder than that of the trunks or roots of trees. This can
be easily tried in iron furnaces, where a fire of fagots or branches
of trees is of little service. Next follows the flame of oil, tallow,
wax, and the like oily and fat substances, which are not very violent.
But a most powerful heat is found in pitch and rosin, and a still
greater in sulphur, camphor, naphtha, saltpetre, and salts (after they
have discharged their crude matter), and in their compounds; as in
gunpowder, Greek fire (vulgarly called wild fire), and its varieties,
which possess such a stubborn heat as scarcely to be extinguished by
water.

22. We consider that the flame which results from some imperfect metals
is very strong and active; but on all these points further inquiry
should be made.

23. The flame of vivid lightning appears to exceed all the above, so as
sometimes to have melted even wrought iron into drops, which the other
flames cannot accomplish.

24. In ignited bodies there are different degrees of heat, concerning
which, also, a diligent inquiry has not been made. We consider the
faintest heat to be that of tinder, touchwood, and dry rope match,
such as is used for discharging cannon. Next follows that of ignited
charcoal or cinders, and even bricks, and the like; but the most
violent is that of ignited metals, as iron, copper, and the like.
Further inquiry, however, must be made into this also.

25. Some ignited bodies are found to be much warmer than some flames;
for instance, red hot iron is much warmer, and burns more than the
flame of spirits of wine.

26. Some bodies even not ignited, but only heated by the fire, as
boiling water, and the air confined in reverberatories, surpass in heat
many flames and ignited substances.

27. Motion increases heat,[96] as is shown in the bellows and the
blowpipe; for the harder metals are not dissolved or melted by steady
quiet fire, without the aid of the blowpipe.

28. Let an experiment be made with burning-glasses; in which respect I
have observed, that if a glass be placed at the distance of ten inches,
for instance, from the combustible object, it does not kindle or burn
it so readily, as if the glass be placed at the distance of five inches
(for instance), and be then gradually and slowly withdrawn to the
distance of ten inches. The cone and focus of the rays, however, are
the same, but the mere motion increases the effect of the heat.

29. Conflagrations, which take place with a high wind, are thought to
make greater way against than with the wind, because when the wind
slackens, the flame recoils more rapidly than it advances when the wind
is favorable.

30. Flame does not burst out or arise unless it have some hollow
space to move and exert itself in, except in the exploding flame of
gunpowder, and the like, where the compression and confinement of the
flame increase its fury.

31. The anvil becomes so hot by the hammer, that if it were a thin
plate it might probably grow red, like ignited iron by repeated
strokes. Let the experiment be tried.

32. But in ignited bodies that are porous, so as to leave room for the
fire to move itself, if its motion be prevented by strong compression,
the fire is immediately extinguished; thus it is with tinder, or the
burning snuff of a candle or lamp, or even hot charcoal or cinders;
for when they are squeezed by snuffers, or the foot, and the like, the
effect of the fire instantly ceases.

33. The approach toward a hot body increases heat in proportion to the
approximation; a similar effect to that of light, for the nearer any
object is placed toward the light, the more visible it becomes.

34. The[97] union of different heats increases heat, unless the
substances be mixed; for a large and small fire in the same spot tend
mutually to increase each other’s heat, but lukewarm water poured into
boiling water cools it.

35. The continued neighborhood of a warm body increases heat. For the
heat, which perpetually passes and emanates from it, being mixed with
that which preceded it, multiplies the whole. A fire, for instance,
does not warm a room in half an hour as much as the same fire would in
an hour. This does not apply to light, for a lamp or candle placed in
a spot gives no more light by remaining there, than it did at first.

36. The irritation of surrounding cold increases heat, as may be seen
in fires during a sharp frost. We think that this is owing not merely
to the confinement and compression of the heat (which forms a sort
of union), but also by the exasperation of it, as when the air or a
stick are violently compressed or bent, they recoil, not only to the
point they first occupied, but still further back. Let an accurate
experiment, therefore, be made with a stick, or something of the kind,
put into the flame, in order to see whether it be not sooner burned at
the sides than in the middle of it. [98]

37. There are many degrees in the susceptibility of heat. And, first,
it must be observed how much a low gentle heat changes and partially
warms even the bodies least susceptible of it. For even the heat of the
hand imparts a little warmth to a ball of lead or other metal held a
short time in it; so easily is heat transmitted and excited, without
any apparent change in the body.

38. Of all bodies that we are acquainted with, air admits and loses
heat the most readily, which is admirably seen in weather-glasses,
whose construction is as follows: Take a glass with a hollow belly, and
a thin and long neck; turn it upside down, and place it with its mouth
downward into another glass vessel containing water; the end of the
tube touching the bottom of the vessel, and the tube itself leaning a
little on the edge, so as to be fixed upright. In order to do this more
readily, let a little wax be applied to the edge, not, however, so as
to block up the orifice, lest, by preventing the air from escaping, the
motion, which we shall presently speak of, and which is very gentle and
delicate, should be impeded.

Before the first glass be inserted in the other, its upper part (the
belly) should be warmed at the fire. Then upon placing it as we have
described, the air (which was dilated by the heat), after a sufficient
time has been allowed for it to lose the additional temperature, will
restore and contract itself to the same dimensions as that of the
external or common atmosphere at the moment of immersion, and the water
will be attracted upward in the tube to a proportionate extent. A long
narrow slip of paper should be attached to the tube, divided into as
many degrees as you please. You will then perceive, as the weather
grows warmer or colder, that the air contracts itself into a narrower
space in cold weather and dilates in the warm, which will be exhibited
by the rising of the water as the air contracts itself, and its
depression as the air dilates. The sensibility of the air with regard
to heat or cold is so delicate and exquisite, that it far exceeds the
human touch, so that a ray of sunshine, the heat of the breath, and
much more, that of the hand placed on the top of the tube, immediately
causes an evident depression of the water. We think, however, that the
spirit of animals possesses a much more delicate susceptibility of heat
and cold, only that it is impeded and blunted by the grossness of their
bodies.

39. After air, we consider those bodies to be most sensible of heat,
which have been recently changed and contracted by cold, as snow and
ice; for they begin to be dissolved and melt with the first mild
weather. Next, perhaps, follows quicksilver; then greasy substances,
as oil, butter, and the like; then wood; then water; lastly, stones
and metals, which do not easily grow hot, particularly toward their
centre. [99] When heated, however, they retain their temperature for
a very long time; so that a brick or stone, or hot iron, plunged in
a basin of cold water, and kept there for a quarter of an hour or
thereabout, retains such a heat as not to admit of being touched.

40. The less massive the body is, the more readily it grows warm at the
approach of a heated body, which shows that heat with us is somewhat
averse to a tangible mass. [100]

41. Heat with regard to the human senses and touch is various and
relative, so that lukewarm water appears hot if the hand be cold, and
cold if the hand be hot.

XIV. Any one may readily see how poor we are in history, since in the
above tables, besides occasionally inserting traditions and report
instead of approved history and authentic instances (always, however,
adding some note if their credit or authority be doubtful), we are
often forced to subjoin, “Let the experiment be tried--Let further
inquiry be made. ”

XV. We are wont to term the office and use of these three tables the
presenting a review of instances to the understanding; and when this
has been done, induction itself is to be brought into action.
For on an
individual review of all the instances a nature is to be found, such
as always to be present and absent with the given nature, to increase
and decrease with it, and, as we have said, to form a more common
limit of the nature. If the mind attempt this affirmatively from the
first (which it always will when left to itself), there will spring up
phantoms, mere theories and ill-defined notions, with axioms requiring
daily correction. These will, doubtless, be better or worse, according
to the power and strength of the understanding which creates them. But
it is only for God (the bestower and creator of forms), and perhaps
for angels and intelligences, at once to recognize forms affirmatively
at the first glance of contemplation: man, at lest, is unable to do so,
and is only allowed to proceed first by negatives, and then to conclude
with affirmatives, after every species of exclusion.

XVI. We must, therefore, effect a complete solution and separation of
nature; not by fire, but by the mind, that divine fire. The first work
of legitimate induction, in the discovery of forms, is rejection, or
the exclusive instances of individual natures, which are not found in
some one instance where the given nature is present, or are found in
any one instance where it is absent, or are found to increase in any
one instance where the given nature decreases, or the reverse. After an
exclusion correctly effected, an affirmative form will remain as the
residuum, solid, true, and well defined, while all volatile opinions
go off in smoke. This is readily said; but we must arrive at it by a
circuitous route. We shall perhaps, however, omit nothing that can
facilitate our progress.

XVII. The first and almost perpetual precaution and warning which
we consider necessary is this; that none should suppose from the
great part assigned by us to forms, that we mean such forms as the
meditations and thoughts of men have hitherto been accustomed to. In
the first place, we do not at present mean the concrete forms, which
(as we have observed) are in the common course of things compounded
of simple natures, as those of a lion, an eagle, a rose, gold, or the
like. The moment for discussing these will arrive when we come to treat
of the latent process and latent conformation, and the discovery of
them as they exist in what are called substances, or concrete natures.

Nor again, would we be thought to mean (even when treating of simple
natures) any abstract forms or ideas, either undefined or badly defined
in matter. For when we speak of forms, we mean nothing else than those
laws and regulations of simple action which arrange and constitute any
simple nature, such as heat, light, weight, in every species of matter,
and in a susceptible subject. The form of heat or form of light,
therefore, means no more than the law of heat or the law of light.
Nor do we ever abstract or withdraw ourselves from things, and the
operative branch of philosophy. When, therefore, we say (for instance)
in our investigation of the form of heat, Reject rarity, or, Rarity is
not of the form of heat, it is the same as if we were to say, Man can
superinduce heat on a dense body, or the reverse, Man can abstract or
ward off heat from a rare body.

But if our forms appear to any one to be somewhat abstracted, from
their mingling and uniting heterogeneous objects (the heat, for
instance, of the heavenly bodies appears to be very different from that
of fire; the fixed red of the rose and the like, from that which is
apparent in the rainbow, or the radiation of opal or the diamond;[101]
death by drowning, from that by burning, the sword, apoplexy, or
consumption; and yet they all agree in the common natures of heat,
redness, and death), let him be assured that his understanding is
inthralled by habit, by general appearances and hypotheses. For it
is most certain that, however heterogeneous and distinct, they agree
in the form or law which regulates heat, redness, or death; and that
human power cannot be emancipated and freed from the common course
of nature, and expanded and exalted to new efficients and new modes
of operation, except by the revelation and invention of forms of this
nature. But after this[102] union of nature, which is the principal
point, we will afterward, in its proper place, treat of the divisions
and ramifications of nature, whether ordinary or internal and more real.

XVIII. We must now offer an example of the exclusion or rejection
of natures found by the tables of review, not to be of the form of
heat; first premising that not only each table is sufficient for the
rejection of any nature, but even each single instance contained in
them. For it is clear from what has been said that every contradictory
instance destroys a hypothesis as to the form. Still, however, for the
sake of clearness, and in order to show more plainly the use of the
tables, we redouble or repeat the exclusive.

_An Example of the Exclusive Table, or of the Rejection of Natures
from the Form of Heat_

1. On account of the sun’s rays, reject elementary (or terrestrial)
nature.

2. On account of common fire, and particularly subterranean fires
(which are the most remote and secluded from the rays of the heavenly
bodies), reject celestial nature.

3. On account of the heat acquired by every description of substances
(as minerals, vegetables, the external parts of animals, water, oil,
air, etc. ) by mere approximation to the fire or any warm body, reject
all variety and delicate texture of bodies.

4. On account of iron and ignited metals, which warm other bodies, and
yet neither lose their weight nor substance, reject the imparting or
mixing of the substance of the heating body.

5. On account of boiling water and air, and also those metals and other
solid bodies which are heated, but not to ignition, or red heat, reject
flame or light.

6. On account of the rays of the moon and other heavenly bodies (except
the sun), again reject flame or light.

7. On account of the comparison between red-hot iron and the flame of
spirits of wine (for the iron is more hot and less bright, while the
flame of spirits of wine is more bright and less hot), again reject
flame and light.

8. On account of gold and other ignited metals, which are of the
greatest specific density, reject rarity.

9. On account of air, which is generally found to be cold and yet
continues rare, reject rarity.

10. On account of ignited iron,[103] which does not swell in bulk, but
retains the same apparent dimension, reject the absolute expansive
motion of the whole.

11. On account of the expansion of the air in thermometers and the
like, which is absolutely moved and expanded to the eye, and yet
acquires no manifest increase of heat, again reject absolute or
expansive motion of the whole.

12. On account of the ready application of heat to all substances
without any destruction or remarkable alteration of them, reject
destructive nature or the violent communication of any new nature.

13. On account of the agreement and conformity of the effects produced
by cold and heat, reject both expansive and contracting motion as
regards the whole.

14. On account of the heat excited by friction, reject principal
nature, by which we mean that which exists positively, and is not
caused by a preceding nature.

There are other natures to be rejected; but we are merely offering
examples, and not perfect tables.

None of the above natures are of the form of heat; and man is freed
from them all in his operation upon heat.

XIX. In the exclusive table are laid the foundations of true induction,
which is not, however, completed until the affirmative be attained. Nor
is the exclusive table perfect, nor can it be so at first. For it is
clearly a rejection of simple natures; but if we have not as yet good
and just notions of simple natures, how can the exclusive table be made
correct? Some of the above, as the notion of elementary and celestial
nature, and rarity, are vague and ill defined. We, therefore, who are
neither ignorant nor forgetful of the great work which we attempt, in
rendering the human understanding adequate to things and nature, by
no means rest satisfied with what we have hitherto enforced, but push
the matter further, and contrive and prepare more powerful aid for the
use of the understanding, which we will next subjoin. And, indeed, in
the interpretation of nature the mind is to be so prepared and formed,
as to rest itself on proper degrees of certainty, and yet to remember
(especially at first) that what is present depends much upon what
remains behind.

XX. Since, however, truth emerges more readily from error than
confusion, we consider it useful to leave the understanding at liberty
to exert itself and attempt the interpretation of nature in the
affirmative, after having constructed and weighed the three tables of
preparation, such as we have laid them down, both from the instances
there collected, and others occurring elsewhere. Which attempt we are
wont to call the liberty of the understanding, or the commencement of
interpretation, or the first vintage.

_The First Vintage of the Form of Heat_

It must be observed that the form of anything is inherent (as appears
clearly from our premises) in each individual instance in which the
thing itself is inherent, or it would not be a form. No contradictory
instance, therefore, can be alleged. The form, however, is found
to be much more conspicuous and evident in some instances than in
others; in those (for example) where its nature is less restrained
and embarrassed, and reduced to rule by other natures. Such instances
we are wont to term coruscations, or conspicuous instances. We must
proceed, then, to the first vintage of the form of heat.

From the instances taken collectively, as well as singly, the nature
whose limit is heat appears to be motion. This is chiefly exhibited in
flame, which is in constant motion, and in warm or boiling liquids,
which are likewise in constant motion. It is also shown in the
excitement or increase of heat by motion, as by bellows and draughts:
for which see Inst. 29, Tab. 3, and by other species of motion, as in
Inst. 28 and 31, Tab. 3. It is also shown by the extinction of fire
and heat upon any strong pressure, which restrains and puts a stop to
motion; for which see Inst. 30 and 32, Tab. 3. It is further shown
by this circumstance, namely, that every substance is destroyed, or
at least materially changed, by strong and powerful fire and heat:
whence it is clear that tumult and confusion are occasioned by heat,
together with a violent motion in the internal parts of bodies; and
this gradually tends to their dissolution.

What we have said with regard to motion must be thus understood, when
taken as the genus of heat: it must not be thought that heat generates
motion, or motion heat (though in some respects this be true), but
that the very essence of heat, or the substantial self[104] of heat,
is motion and nothing else, limited, however, by certain differences
which we will presently add, after giving some cautions for avoiding
ambiguity.

Sensible heat is relative, and regards man, not universe; and is
rightly held to be merely the effect of heat on animal spirit. It is
even variable in itself, since the same body (in different states of
sensation) excites the feeling of heat and of cold; this is shown by
Inst. 41, Tab. 3.

Nor should we confound the communication of heat or its transitive
nature, by which a body grows warm at the approach of a heated body,
with the form of heat; for heat is one thing and heating another. Heat
can be excited by friction without any previous heating body, and,
therefore, heating is excluded from the form of heat. Even when heat is
excited by the approach of a hot body, this depends not on the form of
heat, but on another more profound and common nature; namely, that of
assimilation and multiplication, about which a separate inquiry must be
made.

The notion of fire is vulgar, and of no assistance; it is merely
compounded of the conjunction of heat and light in any body, as in
ordinary flame and red-hot substances.

Laying aside all ambiguity, therefore, we must lastly consider the true
differences which limit motion and render it the form of heat.

I. The first difference is, that heat is an expansive motion, by which
the body strives to dilate itself, and to occupy a greater space than
before. This difference is principally seen in flame, where the smoke
or thick vapor is clearly dilated and bursts into flame.

It is also shown in all boiling liquids, which swell, rise, and boil
up to the sight, and the process of expansion is urged forward till
they are converted into a much more extended and dilated body than the
liquid itself, such as steam, smoke, or air.

It is also shown in wood and combustibles where exudation sometimes
takes place, and evaporation always.

It is also shown in the melting of metals, which, being very compact,
do not easily swell and dilate, but yet their spirit, when dilated
and desirous of further expansion, forces and urges its thicker parts
into dissolution, and if the heat be pushed still further, reduces a
considerable part of them into a volatile state.

It is also shown in iron or stones, which though not melted or
dissolved, are however softened. The same circumstance takes place in
sticks of wood, which become flexible when a little heated in warm
ashes.

It is most readily observed in air, which instantly and manifestly
expands with a small degree of heat, as in Inst. 38, Tab. 3.

It is also shown in the contrary nature of cold; for cold contracts
and narrows every substance;[105] so that in intense frosts nails fall
out of the wall and brass cracks, and heated glass exposed suddenly to
the cold cracks and breaks. So the air, by a slight degree of cold,
contracts itself, as in Inst. 38, Tab. 3. More will be said of this in
the inquiry into cold.

Nor is it to be wondered at if cold and heat exhibit many common
effects (for which see Inst. 32, Tab. 2), since two differences, of
which we shall presently speak, belong to each nature: although in
the present difference the effects be diametrically opposed to each
other. For heat occasions an expansive and dilating motion, but cold a
contracting and condensing motion.

II. The second difference is a modification of the preceding, namely,
that heat is an expansive motion, tending toward the exterior, but at
the same time bearing the body upward. For there is no doubt that there
be many compound motions, as an arrow or dart, for instance, has both a
rotatory and progressive motion. In the same way the motion of heat is
both expansive and tending upward.

This difference is shown by putting the tongs or poker into the fire.
If placed perpendicularly with the hand above, they soon burn it, but
much less speedily if the hand hold them sloping or from below.

It is also conspicuous in distillations _per descensum_, which men are
wont to employ with delicate flowers, whose scent easily evaporates.
Their industry has devised placing the fire above instead of below,
that it may scorch less; for not only flame but all heat has an upward
tendency.

Let an experiment be made on the contrary nature of cold, whether its
contraction be downward, as the expansion of heat is upward. Take,
therefore, two iron rods or two glass tubes, alike in other respects,
and warm them a little, and place a sponge, dipped in cold water, or
some snow, below the one and above the other. We are of opinion that
the extremities will grow cold in that rod first where it is placed
beneath, as the contrary takes place with regard to heat.

III. The third difference is this; that heat is not a uniform expansive
motion of the whole, but of the small particles of the body; and this
motion being at the same time restrained, repulsed, and reflected,
becomes alternating, perpetually hurrying, striving, struggling, and
irritated by the repercussion, which is the source of the violence of
flame and heat.

But this difference is chiefly shown in flame and boiling liquids,
which always hurry, swell, and subside again in detached parts.

It is also shown in bodies of such hard texture as not to swell or
dilate in bulk, such as red-hot iron, in which the heat is most violent.

It is also shown by the fires burning most briskly in the coldest
weather.

It is also shown by this, that when the air is dilated in the
thermometer uniformly and equably, without any impediment or repulsion,
the heat is not perceptible. In confined draughts also, although they
break out very violently, no remarkable heat is perceived, because
the motion affects the whole, without any alternating motion in the
particles; for which reason try whether flame do not burn more at the
sides than in its centre.

It is also shown in this, that all burning proceeds by the minute pores
of bodies--undermining, penetrating, piercing, and pricking them as if
with an infinite number of needle-points. Hence all strong acids (if
adapted to the body on which they act) exhibit the effects of fire,
from their corroding and pungent nature.

The difference of which we now speak is common also to the nature of
cold, in which the contracting motion is restrained by the resistance
of expansion, as in heat the expansive motion is restrained by the
resistance of contraction.

Whether, therefore, the particles of matter penetrate inward or
outward, the reasoning is the same, though the power be very different,
because we have nothing on earth which is intensely cold.

IV. The fourth difference is a modification of the preceding, namely,
that this stimulating or penetrating motion should be rapid and never
sluggish, and should take place not in the very minutest particles, but
rather in those of some tolerable dimensions.

It is shown by comparing the effects of fire with those of time. Time
dries, consumes, undermines, and reduces to ashes as well as fire, and
perhaps to a much finer degree; but as its motion is very slow, and
attacks very minute particles, no heat is perceived.

It is also shown in a comparison of the dissolution of iron and gold;
for gold is dissolved without the excitement of any heat, but iron with
a vehement excitement of it, although most in the same time, because in
the former the penetration of the separating acid is mild, and gently
insinuates itself, and the particles of gold yield easily, but the
penetration of iron is violent, and attended with some struggle, and
its particles are more obstinate.

It is partially shown, also, in some gangrenes and mortifications of
flesh, which do not excite great heat or pain, from the gentle nature
of the putrefaction.

Let this suffice for a first vintage, or the commencement of the
interpretation of the form of heat by the liberty of the understanding.

From this first vintage the form or true definition of heat (considered
relatively to the universe and not to the sense) is briefly thus--Heat
is an expansive motion restrained, and striving to exert itself in the
smaller particles. [106] The expansion is modified by its tendency to
rise, though expanding toward the exterior; and the effort is modified
by its not being sluggish, but active and somewhat violent.

With regard to the operative definition, the matter is the same. If you
are able to excite a dilating or expansive motion in any natural body,
and so to repress that motion and force it on itself as not to allow
the expansion to proceed equally, but only to be partially exerted and
partially repressed, you will beyond all doubt produce heat, without
any consideration as to whether the body be of earth (or elementary, as
they term it), or imbued with celestial influence, luminous or opaque,
rare or dense, locally expanded or contained within the bounds of its
first dimensions, verging to dissolution or remaining fixed, animal,
vegetable, or mineral, water, or oil, or air, or any other substance
whatever susceptible of such motion. Sensible heat is the same, but
considered relatively to the senses. Let us now proceed to further
helps.

XXI. After our tables of first review, our rejection or exclusive
table, and the first vintage derived from them, we must advance to the
remaining helps of the understanding with regard to the interpretation
of nature, and a true and perfect induction, in offering which we
will take the examples of cold and heat where tables are necessary,
but where fewer instances are required we will go through a variety
of others, so as neither to confound investigation nor to narrow our
doctrine.

In the first place, therefore, we will treat of prerogative
instances;[107] 2. Of the supports of induction; 3. Of the correction
of induction; 4. Of varying the investigation according to the
nature of the subject; 5. Of the prerogative natures with respect to
investigation, or of what should be the first or last objects of our
research; 6. Of the limits of investigation, or a synopsis of all
natures that exist in the universe; 7. Of the application to practical
purposes, or of what relates to man; 8. Of the preparations for
investigation; 9. And lastly, of the ascending and descending scale of
axioms. [108]

XXII. Among the prerogative instances we will first mention solitary
instances. Solitary instances are those which exhibit the required
nature in subjects that have nothing in common with any other subject
than the nature in question, or which do not exhibit the required
nature in subjects resembling others in every respect except that
of the nature in question; for these instances manifestly remove
prolixity, and accelerate and confirm exclusion, so that a few of them
are of as much avail as many.

For instance, let the inquiry be the nature of color. Prisms,
crystalline gems, which yield colors not only internally but on the
wall, dews, etc. , are solitary instances; for they have nothing in
common with the fixed colors in flowers and colored gems, metals,
woods, etc. , except the color itself. Hence we easily deduce that
color is nothing but a modification of the image of the incident and
absorbed light, occasioned in the former case by the different degrees
of incidence, in the latter by the various textures and forms of
bodies. [109] These are solitary instances as regards similitude.

Again, in the same inquiry the distinct veins of white and black in
marble, and the variegated colors of flowers of the same species, are
solitary instances; for the black and white of marble, and the spots of
white and purple in the flowers of the stock, agree in every respect
but that of color. Thence we easily deduce that color has not much to
do with the intrinsic natures of any body, but depends only on the
coarser and as it were mechanical arrangement of the parts. These are
solitary instances as regards difference. We call them both solitary or
wild, to borrow a word from the astronomers.

XXIII. In the second rank of prerogative instances we will consider
migrating instances. In these the required nature passes toward
generation, having no previous existence, or toward corruption, having
first existed. In each of these divisions, therefore, the instances
are always twofold, or rather it is one instance, first in motion or
on its passage, and then brought to the opposite conclusion. These
instances not only hasten and confirm exclusion, but also reduce
affirmation, or the form itself, to a narrow compass; for the form
must be something conferred by this migration, or, on the contrary,
removed and destroyed by it; and although all exclusion advances
affirmation, yet this takes place more directly in the same than in
different subjects; but if the form (as it is quite clear from what
has been advanced) exhibit itself in one subject, it leads to all. The
more simple the migration is, the more valuable is the instance. These
migrating instances are, moreover, very useful in practice, for since
they manifest the form, coupled with that which causes or destroys it,
they point out the right practice in some subjects, and thence there
is an easy transition to those with which they are most allied. There
is, however, a degree of danger which demands caution, namely, lest
they should refer the form too much to its efficient cause, and imbue,
or at least tinge, the understanding with a false notion of the form
from the appearance of such cause, which is never more than a vehicle
or conveyance of the form. This may easily be remedied by a proper
application of exclusion.

Let us then give an example of a migrating instance. Let whiteness be
the required nature. An instance which passes toward generation is
glass in its entire and in its powdered state, or water in its natural
state, and when agitated to froth; for glass when entire, and water in
its natural state, are transparent and not white, but powdered glass
and the froth of water are white and not transparent. We must inquire,
therefore, what has happened to the glass or water in the course of
this migration; for it is manifest that the form of whiteness is
conveyed and introduced by the bruising of the glass and the agitation
of the water; but nothing is found to have been introduced but a
diminishing of the parts of the glass and water and the insertion
of air. Yet this is no slight progress toward discovering the form
of whiteness, namely, that two bodies, in themselves more or less
transparent (as air and water, or air and glass), when brought into
contact in minute portions, exhibit whiteness from the unequal
refraction of the rays of light.

But here we must also give an example of the danger and caution of
which we spoke; for instance, it will readily occur to an understanding
perverted by efficients, that air is always necessary for producing the
form of whiteness, or that whiteness is only generated by transparent
bodies, which suppositions are both false, and proved to be so by
many exclusions; nay, it will rather appear (without any particular
regard to air or the like), that all bodies which are even in such of
their parts as affect the sight exhibit transparency, those which are
uneven and of simple texture whiteness, those which are uneven and of
compound but regular texture all the other colors except black, but
those which are uneven and of a compound irregular and confused texture
exhibit blackness. An example has been given, therefore, of an instance
migrating toward generation in the required nature of whiteness. An
instance migrating toward corruption in the same nature is that of
dissolving froth or snow, for they lose their whiteness and assume the
transparency of water in its pure state without air.

Nor should we by any means omit to state, that under migrating
instances we must comprehend not only those which pass toward
generation and destruction, but also those which pass toward increase
or decrease, for they, too, assist in the discovery of the form, as is
clear from our definition of a form and the Table of Degrees. Hence
paper, which is white when dry, is less white when moistened (from
the exclusion of air and admission of water), and tends more to
transparency. The reason is the same as in the above instances. [110]

XXIV. In the third rank of prerogative instances we will class
conspicuous instances, of which we spoke in our first vintage of the
form of heat, and which we are also wont to call coruscations, or free
and predominant instances. They are such as show the required nature
in its bare substantial shape, and at its height or greatest degree
of power, emancipated and free from all impediments, or at least
overcoming, suppressing, and restraining them by the strength of its
qualities; for since every body is susceptible of many united forms of
natures in the concrete, the consequence is that they mutually deaden,
depress, break, and confine each other, and the individual forms are
obscured. But there are some subjects in which the required nature
exists in its full vigor rather than in others, either from the absence
of any impediment, or the predominance of its quality. Such instances
are eminently conspicuous. But even in these care must be taken, and
the hastiness of the understanding checked, for whatever makes a show
of the form, and forces it forward, is to be suspected, and recourse
must be had to severe and diligent exclusion.

For example, let heat be the required nature. The thermometer is a
conspicuous instance of the expansive motion, which (as has been
observed) constitutes the chief part of the form of heat; for although
flame clearly exhibits expansion, yet from its being extinguished every
moment, it does not exhibit the progress of expansion. Boiling water
again, from its rapid conversion into vapor, does not so well exhibit
the expansion of water in its own shape, while red-hot iron and the
like are so far from showing this progress, that, on the contrary, the
expansion itself is scarcely evident to the senses, on account of its
spirit being repressed and weakened by the compact and coarse particles
which subdue and restrain it.