16. All bodies rubbed violently, as stone, wood, cloth, etc., so that
rudders, and axles of wheels, sometimes catch fire, and the West
Indians obtain fire by attrition.
17. Green and moist vegetable matter confined and rubbed together,
as roses, peas in baskets; so hay, if it be damp when stacked, often
catches fire.
18. Quicklime sprinkled with water.
19. Iron, when first dissolved by acids in a glass, and without any
application to fire; the same of tin, but not so intensely.
20. Animals, particularly internally; although the heat is not
perceivable by the touch in insects, on account of their small size.
21. Horse dung, and the like excrement from other animals, when fresh.
22. Strong oil of sulphur and of vitriol exhibit the operation of heat
in burning linen.
23. As does the oil of marjoram, and like substances, in burning the
bony substance of the teeth.
24. Strong and well rectified spirits of wine exhibit the same effects;
so that white of eggs when thrown into it grows hard and white, almost
in the same manner as when boiled, and bread becomes burned and brown
as if toasted.
25. Aromatic substances and warm plants, as the dracunculus [arum], old
nasturtium, etc., which, though they be not warm to the touch (whether
whole or pulverized), yet are discovered by the tongue and palate to be
warm and almost burning when slightly masticated.
26. Strong vinegar and all acids, on any part of the body not clothed
with the epidermis, as the eye, tongue, or any wounded part, or where
the skin is removed, excite a pain differing but little from that
produced by heat.
27. Even a severe and intense cold produces a sensation of burning.[83]
“Nec Boreæ penetrabile frigus adurit.”
28. Other instances.
We are wont to call this a table of existence and presence.
XII. We must next present to the understanding instances which do not
admit of the given nature, for form (as we have observed) ought no less
to be absent where the given nature is absent, than to be present where
it is present. If, however, we were to examine every instance, our
labor would be infinite.
Negatives, therefore, must be classed under the affirmatives, and the
want of the given nature must be inquired into more particularly in
objects which have a very close connection with those others in which
it is present and manifest. And this we are wont to term a table of
deviation or of absence in proximity.
_Proximate Instances wanting the Nature of Heat_
The rays of the moon, stars, and comets, are not found to be warm to
the touch, nay, the severest cold has been observed to take place
at the full of the moon. Yet the larger fixed stars are supposed to
increase and render more intense the heat of the sun, as he approaches
them, when the sun is in the sign of the Lion, for instance, and in the
dog-days.[84]
The rays of the sun in what is called the middle region of the air
give no heat, to account for which the commonly assigned reason is
satisfactory; namely, that that region is neither sufficiently near to
the body of the sun whence the rays emanate, nor to the earth whence
they are reflected. And the fact is manifested by snow being perpetual
on the tops of mountains, unless extremely lofty. But it is observed,
on the other hand, by some, that at the Peak of Teneriffe, and also
among the Andes of Peru, the tops of the mountains are free from snow,
which only lies in the lower part as you ascend. Besides, the air on
the summit of these mountains is found to be by no means cold, but only
thin and sharp; so much so, that in the Andes it pricks and hurts the
eyes from its extreme sharpness, and even excites the orifice of the
stomach and produces vomiting. The ancients also observed, that the
rarity of the air on the summit of Olympus was such, that those who
ascended it were obliged to carry sponges moistened with vinegar and
water, and to apply them now and then to their nostrils, as the air was
not dense enough for their respiration; on the summit of which mountain
it is also related, there reigned so great a serenity and calm, free
from rain, snow, or wind, that the letters traced upon the ashes of the
sacrifices on the altar of Jupiter, by the fingers of those who had
offered them, would remain undisturbed till the next year. Those even,
who at this day go to the top of the Peak of Teneriffe, walk by night
and not in the daytime, and are advised and pressed by their guides, as
soon as the sun rises, to make haste in their descent, on account of
the danger (apparently arising from the rarity of the atmosphere), lest
their breathing should be relaxed and suffocated.[85]
The reflection of the solar rays in the polar regions is found to
be weak and inefficient in producing heat, so that the Dutch, who
wintered in Nova Zembla, and expected that their vessel would be
freed about the beginning of July from the obstruction of the mass of
ice which had blocked it up, were disappointed and obliged to embark
in their boat. Hence the direct rays of the sun appear to have but
little power even on the plain, and when reflected, unless they are
multiplied and condensed, which takes place when the sun tends more
to the perpendicular; for, then, the incidence of the rays occurs at
more acute angles, so that the reflected rays are nearer to each other,
while, on the contrary, when the sun is in a very oblique position,
the angles of incidence are very obtuse, and the reflected rays at a
greater distance. In the meantime it must be observed, that there may
be many operations of the solar rays, relating, too, to the nature of
heat, which are not proportioned to our touch, so that, with regard to
us, they do not tend to produce warmth, but, with regard to some other
bodies, have their due effect in producing it.
Let the following experiment be made. Take a lens the reverse of a
burning-glass, and place it between the hand and the solar rays, and
observe whether it diminish the heat of the sun as a burning-glass
increases it. For it is clear, with regard to the visual rays, that in
proportion as the lens is made of unequal thickness in the middle and
at its sides, the images appear either more diffused or contracted. It
should be seen, therefore, if the same be true with regard to heat.
Let the experiment be well tried, whether the lunar rays can be
received and collected by the strongest and best burning-glasses, so as
to produce even the least degree of heat.[86] But if that degree be,
perhaps, so subtile and weak, as not to be perceived or ascertained
by the touch, we must have recourse to those glasses which indicate
the warm or cold state of the atmosphere, and let the lunar rays fall
through the burning-glass on the top of this thermometer, and then
notice if the water be depressed by the heat.[87]
Let the burning-glass be tried on warm objects which emit no luminous
rays, as heated but not ignited iron or stone, or hot water, or the
like; and observe whether the heat become increased and condensed, as
happens with the solar rays.
Let it be tried on common flame.
The effect of comets (if we can reckon them among meteors[88]) in
augmenting the heat of the season is not found to be constant or
clear, although droughts have generally been observed to follow them.
However, luminous lines, and pillars, and openings, and the like,
appear more often in winter than in summer, and especially with the
most intense cold but joined with drought. Lightning, and coruscations,
and thunder, however, rarely happen in winter; and generally at the
time of the greatest heats. The appearances we term falling stars are
generally supposed to consist of some shining and inflamed viscous
substance, rather than of violently hot matter; but let this be further
investigated.
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.