This is the tenth post in the Novum Organum sequence. For context, see the sequence introduction. For the reading guide, see earlier posts in the sequence.

We have used Francis Bacon's Novum Organum in the version presented at www.earlymoderntexts.com. Translated by and copyright to Jonathan Bennett. Prepared for LessWrong by Ruby.

[[Bacon has begun demonstrating his scientific method in earnest. He uses the investigation of the nature of heat as his example. He explains that his approach works by compiling a natural history, i.e., data related to phenomena of interested which he arranges into three tables:

1) A table of presence which lists many examples where phenomena of interest in presence, e.g. many examples of things where we have heat. Bacon is quite thorough.

2) A table of nearby essence. To discriminate the true cause of heat, Bacon looks for examples of things that resemble those in the table of presence yet are lacking the heat. For the example, the light of the moon (cold) is contrasted with the light of the sun (hot) which is interesting given they are both heavenly bodies.

3) A table of degrees or comparison where are examples are brought where the amount of perceived heat differs in degree between things. This is also useful in discriminating the true underlying cause and and nature of heat.

Bacon is thorough in his examples here, listing an extreme variety of things. To his credit, he eventually hits upon that heat is about motion.

One the hand, these passages can be see as boring, but I see them as quite fascinating– it's remarkable to see how on the earlier pioneers of modern science thought and approached solving what to him was a great mystery. He did not rush, he did not get bored, instead he painstakingly collected his data. A superb demonstration of empiricism.]]

Aphorism Concerning the Interpretation of Nature: Book 2: 10-14

10. Having looked at doctrines, we must go on to precepts, dealing with them in the most direct way and not getting things the wrong way around. Guides for the interpretation of nature are of two fundamental kinds: (1) how to draw or fetch up axioms from experience; (2) how to get from axioms to new experiments. Precepts of kind (1) divide into three kinds of service: (i) catering to the senses, (ii) catering to the memory, and (iii) catering to the mind or reason. (i) First of all we must prepare an adequate and sound natural and experimental history, this being the basis for everything, for we are not to •imagine or •suppose but to •discover what nature makes or does. [Bacon doesn’t return to (ii) memory.] (iii) But natural and experimental history is so various and diffuse that it confuses and scatters the intellect unless it is kept short and set out in a suitable order. So we must create tables and arrangements of instances that are done in such a way that the intellect can act on them. And even when this is done, the unaided and unguided intellect hasn’t the competence to form axioms. Therefore in the third place we must use induction, true and legitimate induction, which is the very key of interpretation. But I must deal first with this ·induction·, though it comes last, and then I shall go back to the others.

[In fact, all the rest of the work has to do with what Bacon calls ‘induction’.]

11. The investigation of forms proceeds in this way: For a given nature, we must first turn our minds to all known instances that agree in having this nature (they’ll differ greatly in other ways). This collection is to be made in the manner of a ·natural· history, with no rush to theorize about it and with no great amount of subtlety. If for example we are to investigate the form of heat, we need a table of instances of heat. This is my First Table:

1. The rays of the sun, especially in summer and at noon.

2. The sun’s rays reflected and condensed. . . .especially in burning glasses and mirrors.

3. Fiery meteors.

4. Lightning.

5. Eruptions of flame from the cavities of mountains.

6. All flame.

7. Burning solids.

8. Natural warm baths.

9. Hot or boiling liquids.

10. Hot vapours and fumes, and even air that becomes furiously hot if it is confined, as in reverbatory furnaces.

11. Weather that is clear and bright just because of the constitution of the air, without reference to the time of year.

12. Air that is confined and underground in some caverns, especially in winter.

13. All shaggy substances—wool, skins of animals, down of birds—have some warmth.

14. All bodies, whether solid or liquid, dense or rare (as air is), held for a time near a fire.

15. Sparks from flint and steel that are struck hard.

16. All bodies—stone, wood, cloth, etc.—when rubbed strongly (axles of wheels sometimes catch fire; and rubbing was how they kindled fire in the West Indies).

17. Green and moist plants jammed together, as roses or peas in baskets (hay in a damp haystack often catches fire).

18. Quicklime sprinkled with water.

19. Iron when first dissolved in aqua fortis [= nitric acid] in a test tube without being put near a fire (the same with tin, though not with the same intensity).

20. Animals, especially their insides (and always their insides), though we don’t feel the heat in insects because they are so small.

21. Freshly dropped horse dung and other animal excrements.

22. Strong oil of sulphur and of vitriol has the effect of heat when it scorches linen.

23. Oil of marjoram and similar oils have the effect of heat in burning the bones of the teeth.

24. Strong alcohol acts as though it were hot: it makes egg-white congeal and turn white, as though it were cooked; it makes bread crusty, like toast.

25. Aromatic and hot herbs. . . .although not warm to the hand. . . .feel hot to the palate when they are chewed.

26. When strong vinegar or any acid is applied to parts of the body that don’t have skin—the eye, the tongue, or on any part that has been damaged and lost some skin—it produces a pain like the pain heat produces.

27. Even keen and intense cold produces a kind of sensation of burning. . . .

28. Other instances.

I call this the Table of Essence and Presence.

12. Secondly, we must turn our minds to instances where the given nature is lacking, because—as I said above—the form should not only be present when the given nature is present but also be absent when the nature is absent. But a list of these would be endless! So the negatives should be linked with the affirmatives: we shall look into the absence of the given nature only in things that are most like ones where the nature is present and apparent. I call this, which is my Second Table, the Table of Divergence or of Nearby Absence. These are instances where the nature of heat is absent but which are in other ways close to ones where it is present.

[Each tag of the form #n means that the topic is negative instances that are nearby to positive instance n.]

1. (#1) The rays of the moon and of stars and comets are not found to be hot to the touch; indeed the severest colds are experienced at the full moons. The larger fixed stars, however, when passed or approached by the sun, are thought to increase and intensify the heat of the sun. . . .

2. (#2) The rays of the sun in the so-called ‘middle region’ of the air don’t give heat. (The usual explanation for this is pretty good: namely, that region is far enough away from the body of the sun that gives off the rays and from the earth that reflects them.) And this appears from the fact that on mountain-tops there is perpetual snow, unless they are very high: it has been observed that on the Peak of Tenerife and among the Andes of Peru the summits of the mountains are free from snow though there is snow a little way below the summits. Actually, the air at the very top is not found to be at all cold, but only thin and sharp—so much so that in the Andes it pricks and hurts the eyes by its excessive sharpness and also irritates the entrance to the stomach, producing vomiting. The ancients observed that on the summit of Olympus the air was so thin that those who climbed it had to carry sponges with them dipped in vinegar and water, and to apply them from time to time to the mouth and nose, because the air was too thin to support respiration. They also reported that on this summit the air was so serene, and so free from rain and snow and wind, that words written by the finger in the ashes of a sacrifice were still there, undisturbed, a year later. . . .

3. (#2) The reflection of the sun’s rays in regions near the polar circles is found to be very weak and ineffective in producing heat: the Dutch who wintered in Nova Zembla and expected their ship to be freed by the beginning of July from the mass of ice that hemmed it in were disappointed in their hopes and forced to take to their row-boats. It seems, then, that the direct rays don’t have much power, even down at sea level; and don’t reflect much either, except when they are many of them combined. That is what happens when the sun moves high in the sky, for then the incident rays meet the earth at acuter angles, so that the lines of the rays are nearer each other; whereas when the sun ·is lower in the sky and so· shines very obliquely, the angles are very obtuse which means that the lines of rays are further from one another. Meanwhile, bear in mind that the sun may do many things, including ones that involve the nature of heat, that don’t register on our sense of touch—things that we won’t experience as detectable warmth but that have the effect of heat on some other bodies.

4. (#2) Try the following experiment. Take a glass made in the opposite manner to an ordinary burning glass, let the sun shine through it onto your hand, and observe whether it •lessens the heat of the sun as a burning glass •increases and intensifies it. It’s quite clear what happens with optical rays ·shone through a glass·: according as the middle of the glass is thicker or thinner than the sides, the objects seen through it appear more spread or more contracted. Well, see whether the same holds for heat.

5. (#2) Try to find out whether by means of the strongest and best built burning glasses the rays of the moon can be caught and collected in such a way as to produce some warmth, however little. In case the warmth produced is too weak to be detected by the sense of touch, use one of those glasses that indicate the state of the atmosphere in respect to heat and cold: let the moon’s rays fall through the ·extra-powerful· burning glass onto the top of a glass of this kind, and then see whether the water sinks because of warmth.

[The ‘glasses’ in question are thermometers; see item 38 for Bacon’s instructions on how to make and use one.]

6. (#2) Try a burning glass with a source of heat that doesn’t emit rays or light—such as iron or stone that has been heated but not ignited, or boiling water, or the like. Observe whether the burning glass produces an increase of the heat as it does with the sun’s rays.

7. (#2) Try a burning glass also with ordinary flame.

8. (#3) Comets (if we are to count these as meteors) aren’t found to exert a constant and detectable effect in increasing the heat of the season, though they have been seen often to be followed by droughts. Moreover bright beams and pillars and openings in the heavens appear oftener in winter than in summertime, especially during the intensest cold but always accompanied by dry weather. (#4) Lightning-flashes and thunderclaps seldom occur in the winter, but rather at times of great heat. So-called ‘falling stars’ are commonly thought to consist of some thick and highly incandescent liquid rather than to be of any strong fiery nature. But this should be further looked into.

9. (#4) Certain flashes give light but don’t burn; and these always come without thunder.

10. (#5) Discharges and eruptions of flame occur just as frequently in cold as in warm countries, e.g. in Iceland and Greenland. In cold countries, too, many of the trees—e.g. fir, pine and others—are more inflammable, more full of pitch and resin, than the trees in warm countries. This is an affirmative instance ·of heat·; I can’t associate it with a ·nearby· negative instance because not enough careful work has been done on the locations and soil-conditions in which eruptions of this kind usually occur.

11. (#6) All flame, always, is more or less warm; there are no ·nearby· negative instances to be cited here. [Bacon then cites seven kinds of situation in which there are something like flames but little if any detected heat. He says, for example, that a sweaty horse when seen at night is faintly luminous. Then:]

12. (#7) Every body that is subjected to heat that turns it to a fiery red is itself hot, even if there are no flames; there are no ·nearby· negative instances to go with this affirmative. . . .

13. (#8) Not enough work has been done on the locations and soil-conditions in which warm baths usually arise; so no ·nearby· negative instance is cited.

14. (#9) To boiling liquids I attach the negative instance of liquid in its own nature. We don’t find any tangible liquid that is warm in its own nature and remains so constantly; the warmth always comes from something outside the liquid and is possessed by the liquid only temporarily. The water in natural warm baths ·is not inherently warm; when it· is taken from its spring and put into a container, it cools down just like water that has been heated on a fire. The liquids whose power and way of acting makes them the hottest and that eventually burn—e.g. alcohol, chemical oil of spices, oil of vitriol and of sulphur, and the like—are at first cold to the touch; though oily substances are less cold to the touch than watery ones, oil being less cold than water, as silk ·is less cold· than linen. But this belongs to the Table of Degrees of Cold.

15. (#10) Similarly, to hot vapour I attach the negative instance of the nature of vapour itself as we experience it. For although the vapours given off by oily substances are easily flammable, they aren’t found to be warm unless they have only recently been given off by a body that is warm.

16. (#10) Similarly, to hot air I attach the negative instance of the nature of air itself. For in our regions we don’t find any air that is warm, unless it has either been confined or subjected to friction or obviously warmed by the sun, fire, or some other warm substance.

17. (#11) I here attach the negative instance of weather that is colder than is suitable for the season of the year, which in our regions occurs during east and north winds; just as we have weather of the opposite kind with the south and west winds. . . .

18. (#12) Here I attach the negative instance of air confined in caverns during the summer. But air in confinement is something that needs to be looked into more carefully ·than has so far been done·. For one thing, it isn’t certain what is the nature of air in itself in relation to heat and cold. It’s clear that air gets warmth from the influence of the heavenly bodies, and cold perhaps from the exhalations of the earth and in the so-called ‘middle region’ of air from cold vapours and snow. So that we can’t form an opinion about the nature of air by examining the open air that is all around us; but we might do better by examining it when confined. But the air will have to be confined in something that won’t communicate warmth or cold to the air from itself, and won’t easily let the outer atmosphere affect the confined air. So do an experiment using an earthenware jar wrapped in many layers of leather to protect it from the outer air; let the vessel remain tightly closed for three or four days; then open it and test the level of heat or cold either by touch or by a thermometer.

19. (#13) There’s also a question as to whether the warmth in wool, skins, feathers and the like comes from •a faint degree of heat that they have because they came from animals, or from •some kind of fat or oil that has a nature like warmth; or simply (as I suggested in the preceding paragraph) from •the air’s being confined and segregated. For all air that is cut off from the outer air seems to have some warmth. So: try an experiment with fibres made of linen, not of such animal products as wool, feathers or silk. It is also worth noting that when something is ground to a powder, the powder (which obviously has air enclosed in it) is less cold than the intact substance from which it was made; and in the same way I think that all froth (which contains air) is less cold than the liquid it comes from.

20. (#14) I don’t attach any negative to this because everything around us, whether solid or gaseous, gets warm when put near fire. They differ in this way, though: some substances (such as air, oil and water) warm up more quickly than others (such as stone and metal). But this belongs to the Table of Degrees.

21. (#15) I don’t attach any negative to this either, except that it should be noted that •sparks are produced from flint and iron and the like only when tiny particles are struck off from the substance of the stone or metal; that •you can’t get sparks by whirling something through the air, as is commonly supposed; and that •the sparks themselves, owing to the weight of the body from which they are struck, tend downwards rather than upwards, and when they are extinguished they become a tangible sooty substance.

22. (#16) I don’t think there is any negative to attach to this instance. For every solid body in our environment clearly becomes warmer when it is rubbed; so that the ancients thought (dreamed!) that the heavenly bodies’ only way of gaining heat was by their rubbing against the air as they spun. On this subject we must look into whether bodies discharged from ·military· engines, such as cannon-balls, don’t acquire some heat just from the blast, so as to be found somewhat warm when they fall. But moving air chills rather than warms, as appears from wind, bellows, and blowing with the lips close together. It isn’t surprising that this sort of motion doesn’t generate heat: it isn’t rapid enough, and it involves a mass moving ·all together· rather than particles ·moving in relation to one another·.

23. (#17) This should be looked into more thoroughly. It seems that green and moist grass and plants have some heat hidden in them, but it is so slight that it isn’t detectable by touch in any individual ·carrot or cabbage·. But then a lot of them are collected and shut up together, their gases aren’t sent out into the atmosphere but can interact with one another, producing palpable heat and sometimes flame.

24. (#18) This too needs to looked into more thoroughly. For quicklime sprinkled with water seems to become hot either •by the concentration of heat that was previously scattered (as in the (23) case of confined plants) or •because the fiery gas is excited and roughed up by the water so that a struggle and conflict is stirred up between them. Which of these two is the real cause will appear more readily if oil is poured on ·the quicklime· instead of water; for oil will concentrate the enclosed gases just as well as water does, but it won’t irritate it in the same way. We should also broaden the experiment •by employing the ashes and cinders of bodies other than quicklime, and dousing them with liquids other than water.

25. (#19) The negative that I attach to this instance is: other metals, ones that are softer and more fusible. When gold leaf is dissolved in aqua regia it gives no heat to the touch; nor does lead dissolved in nitric acid; nor again does mercury (as I remember), though silver does, and copper too (as I remember); tin still more obviously; and most of all iron and steel, which not only arouse a strong heat when they dissolve but also a vigorous bubbling. So it seems that the heat is produced by conflict: the aqua fortis penetrates the substance, digging into it and tearing it apart, and the substance resists. With substances that yield more easily hardly any heat is aroused.

26. (#20) I have no negative instances to attach to the heat of animals, except for insects (as I have remarked) because of their small size. Fish are found to have less heat than land animals do, but not a complete absence of heat. Plants have no heat that can be felt by touch, either in their sap or in their pith when freshly opened up. The heat in an animal varies from one part of it to another (there are different degrees of heat around the heart, in the brain, and on the skin) and also from one event to another—e.g. ·the animal’s heat increases· when it engages in strenuous movements or has a fever.

27. (#21) It’s hard to attach a negative to this instance. Indeed animal dung obviously has potential heat ·even· when no longer fresh; this can be seen from how it enriches the soil.

28. (#22 and #23) Liquids, whether waters or oils, that are intensely caustic act as though they were hot when they break into bodies and, after a while, burn them; but they don’t feel hot at first. But how they operate depends on what they are operating on. . . . Thus, aqua regia dissolves gold but not silver; nitric acid dissolves silver but not gold; neither dissolves glass, and so on with others.

29. (#24) Try alcohol on wood, and also on butter, wax and pitch; and observe whether it has enough heat to melt any of them. For 24 shows it exhibiting a power that resembles heat in making bread crusty. Also, find out what it can do in the way of liquefying substances. Experiment with a thermometer or calendar glass, hollow at the top; pour some well-distilled alcohol into the hollow; cover it so that the spirit keeps its heat better; and observe whether by its heat it makes the water go down. [A ‘calendar glass’ is a thermometer. See item 38].

30. (#25) Spices and sharp-tasting herbs are hot to the palate and much hotter to the stomach. So we should see on what other substances they act as though they were hot. (Sailors report that when large quantities of spices are kept shut up tightly for a long time and then suddenly opened, those who first disturb and take them out are at risk of fever and inflammation.) Something else that can be tested: whether such spices and herbs in a powdered form will dry bacon and meat hung over them, as smoke does.

31. (#26) Cold things such as vinegar and oil of vitriol are corrosive and penetrating, just as are hot things such as oil of marjoram and the like. Both alike cause pain in living things, and tear apart and consume things that are inanimate. There is no negative to attach to this ·positive· instance. A further point: whenever an animal feels pain it has a certain sensation of heat.

[A warning about ‘inanimate’: it translates non animatus, which strictly means ‘not breathing’, and Bacon often uses it to cover plants as well as things that are ‘inanimate’ in our sense. This version will stay with ‘inanimate’ except in one place where ‘non-animal’ is required.]

32. (#27) In many contexts heat and cold have the same effect, though for different reasons. Boys find that after a while snow seems to burn their hands; cold preserves meat from going rotten just as fire does; and heat makes bodies shrink, which cold does also. But these and similar instances are better dealt with in the investigation of cold.

13. ·We have dealt with firstly (11) a Table of Essence and Presence, secondly (12) a Table of Divergence or of Nearby Absence. Now·, thirdly, we must turn our minds to instances in which the nature being investigated is found in different degrees, greater or lesser; either by comparing the amounts of it that a single thing has at different times or by comparing the amounts of it that different things have. The •form of a thing is the very •thing itself; the only difference between the thing and the form is just that between

the thing and the form

is just that between

the apparent and the real,
the external and the internal, or
the thing in reference to man and the thing in reference to the universe.

From this is rigorously follows that no •nature should be accepted as the true •form unless it—·i.e. the thing whose nature is in question·—always decreases when the nature decreases, and increases when the nature increases. So I call this—my Third Table—the Table of Degrees or the Table of Comparison.

Here is my Table of Degrees or of Comparison, in relation to Heat. I start with substances that contain no degree of heat that can be felt by touch but seem to have a certain potential heat—a disposition and readiness to be hot. Then I shall move on to substances that are actually hot—hot to the touch—and to their intensities and degrees.

1. We don’t encounter any solid, tangible things that just are hot in their own natures. No stone, metal, sulphur, fossil, wood, water or animal carcass is found to be hot. The water in ·naturally· hot baths seems to be heated by external causes—either by flames or subterraneous hot material such as is thrown up from Etna and many other mountains, or by bodies colliding as when iron or tin is ground to powder and heat is caused. Thus, there is no heat detectable by touch in non-living substances; though they differ in how cold they are—wood isn’t as cold as metal. But that belongs to the Table of Degrees of Coldness.

2. However, many inanimate substances—such as sulphur, naphtha and oil extracted from rocks—have a lot of potential heat and are strongly disposed to burst into flame.

3. ·Some· substances that have been hot continue to have some of their former heat lurking in them. Examples of this are horse dung retaining the heat of the horse, also lime (and perhaps also ashes and soot) retaining the heat of the fire. . . .

4. As for the vegetable kingdom: no plant or part of a plant (such as sap or pith) is warm to the human touch. But as I have already remarked, green plants become warm when they are shut up; and some plants are warm and others cold, this being detectable by the internal touch ·as I call it· of the palate or stomach, and even to touch by external parts of the body ·such as the hands·. It takes a little time for this to develop; we see it at work in poultices and ointments.

5. We don’t find anything warm to the touch in the parts of animals that have died, or in parts that they have excreted. Not even horse dung retains its heat unless it is enclosed and buried. Yet all dung seems to have potential heat, as is seen in how it enriches the fields. Similarly, the carcasses of animals have some such hidden potential heat. A result of this is that in cemeteries where burials take place daily the earth collects a certain hidden heat which consumes a newly buried body much faster than pure earth would. . . .

6. Substances that enrich the soil, such as dung of all kinds, chalk, sea sand, salt and the like, have some disposition to become hot.

7. When anything rots, there are the beginnings of slight heat, but not enough to be detectable by touch. Even the substances which when they putrefy break up into little animals (meat, cheese, etc.) don’t feel warm to the touch; nor does rotten wood, which shines in the dark, feel warm to the touch. In rotting substances, though, heat sometimes announces itself by strong nasty smells.

8. The lowest degree of heat among things that feel warm to the touch seems to be the heat of animals, which varies over quite a wide range. At the bottom of the scale, as in insects, the heat is hardly perceptible to the touch; and the highest scarcely equals the heat the sun gives off in the hottest countries and seasons, and isn’t too great to be tolerated by the hand. But it is said of Constantius, and of some others who had a very dry constitution and bodily condition, that in acute fevers they became so hot as to burn slightly any hand that touched them.

9. Animals increase in heat by motion and exercise, wine and eating, sex, burning fevers, and pain.

10. When attacked by intermittent fevers, animals are at first seized with cold and shivering, but soon after they become exceedingly hot; and in burning and pestilential fevers they are very hot right from the start.

11. We should investigate the different degrees of heat indifferent ·broad kinds of· animals, such as fish, quadrupeds, snakes, birds; and also according to their ·narrower· species, such as lion, vulture, man. ·This would be, among other things, a check on popular beliefs·. For fish are generally thought to be the coldest internally, and birds—especially doves, hawks and sparrows—to be very hot.

12. We should also investigate the different degrees of heat in the different parts of the same animal. For milk, blood, semen and ova are found to be only mildly warm—cooler than the outer flesh of the animal when it is moving or agitated—but no-one has yet investigated what the temperature is in the brain, stomach, heart, etc.

13. In winter and cold weather all animals are cold externally, but internally they are thought to be even warmer ·than at other times·.

14. Even in the hottest countries and at the hottest times of the year and day, the heavenly bodies don’t give off enough heat to kindle a flame in the driest wood or straw or even cloth, except when the heat is increased by burning glasses. But it can raise steam from moist matter.

15. Astronomers have a traditional belief that some stars are hotter than others. Of the planets, Mars is regarded as the hottest after the sun; then comes Jupiter, and then Venus. The moon is said to be cold and Saturn the coldest of all. Of fixed stars, Sirius is said to be the hottest, then Cor Leonis (or Regulus), then the Dog-star, and so on.

16. The sun gives off more heat the nearer it comes to the perpendicular [= ‘to being straight overhead’]; and this is probably true of the other planets also, within their own ranges of temperature. Jupiter, for instance, feels warmer when it is under Cancer or Leo than when it is under Capricorn or

17. The sun and the other planets can be expected to give more heat when they are closest to the earth than when they are furthest away. If it should happen that in some region the sun is at its closest and also near the perpendicular, it would have to give off more heat there than in a region where it is also at its closest but is shining more obliquely. So there should be a study of ·the heat-effects of· the planets in different regions according to how high or low in the sky they are.

18. The sun and other planets are thought to give more heat when nearer to the larger fixed stars. When the sun is in ·the constellation· Leo it is nearer to ·the stars· Cor Leonis, Cauda Leonis, Spica Virginis, Sirius and the Dog-star than when it is in ·the constellation· Cancer, though in the latter position it is nearer to the perpendicular ·and thus has one factor making for less heat and another making for more·. And we have to think that the parts of the sky that are furnished with the most stars, especially big ones, give off the greatest heat, though it isn’t all perceptible to the touch.

19. Summing up: the heat given off by the heavenly bodies is increased in three ways—•by perpendicularity, •by nearness to the earth, and •by the company of stars.

20. The heat of animals, and the heat that reaches us from the heavenly bodies, are much less than

the heat of a flame (even a gentle one) ,
the heat from a burning body, and
the heat of liquids and the air itself when strongly highly heated by fire.

For the flame of alcohol, even when scattered and not concentrated, is still enough to set paper, straw, or linen on fire. The heat of animals will never do that, nor will the sun without a burning-glass.

21. The heat of flames and burning bodies comes in many different intensities; but they haven’t been carefully studied, so I can only skim across the surface of this topic. It seems that the flame of alcohol is the gentlest of all (unless perhaps the will-o’-the-wisp or the flames or sparks from the sweat of animals are even gentler). Next, I think, comes the flame from vegetable matter that is light and porous, such as straw, reeds, and dried leaves—and the flame from hairs or feathers is pretty much the same. Next perhaps comes flame from wood, especially wood containing little resin or tar. ·There is a distinction to be made within the class of flames from that kind of wood·: the flame from small bits of wood such as are commonly tied up in bundles is milder than the flame from trunks and roots of trees. Anyone can see this in the fact that a fire fuelled by bundles of twigs and tree-branches is useless in a furnace for smelting iron. After this, I think, comes flame from oil, tallow, wax and similar fatty and oily substances that aren’t very caustic or corrosive. But the strongest heat comes from tar and resin, and even more from sulphur, camphor, naphtha, rock oil, and salts (after the crude matter is discharged), and from their compounds such as gunpowder, Greek fire (commonly called ‘wildfire’) and its variants, whose heat is so stubborn that it’s hard to extinguish with water.

22. I think that the flame resulting from some imperfect metals is very strong and piercing; but all these things need to be looked into further.

23. The flame of powerful lightning seems to be stronger than any of those others, for it has been known to melt wrought iron into drops, which they can’t do.

24. In burning bodies too there are different degrees of heat, but these haven’t been carefully investigated either. The weakest heat of all, I think, is what comes from the sort of burning linen wick that we use to start fires with, and from the fuses that are used in firing cannons. After this comes burning charcoal made from wood or coal. . . .

[In what follows, a single Latin word is rendered sometimes as ‘red-hot’ and sometimes as ‘burning’, according to the context.]

But I think that red-hot metals—iron, copper etc.—are the hottest of all hot substances. But this needs to be looked into.

25. Some red-hot bodies are found to be much hotter than some flames. Red-hot iron, for instance, is much hotter and more destructive than flame of alcohol.

26. Of substances that aren’t burning but only heated by fire, such as boiling water and air confined in reverbatory furnaces, some are found to be hotter than many flames and burning substances.

27. Motion increases heat, as you can see in bellows and by blowing ·hard into your hand·; so that the way to get a quiet fire to melt one of the harder metals is to take a bellows to it.

28. Try the following experiment with a burning-glass(I am describing it from memory). (1) Place a burning-glass nine inches away from a combustible body. (2) Place the burning-glass at half that distance from the object and then slowly move it back to a distance of nine inches. You will find that the glass doesn’t burn or consume as much of the object in case (1) as it does in case (2). Yet the cone and the focus of the rays are the same in each; it’s the motion that makes the heat more effective.

29. [Omitted. What Bacon wrote doesn’t make physical sense.]

30. Things don’t burst into flames unless the flames have some empty space in which to move and play; except for the explosive flame of gunpowder and the like, where the fire’s fury is increased by its being compressed and imprisoned.

31. An anvil gets very hot under the hammer; so if an anvil were made of a thin plate and were hit with many strong blows from a hammer I would expect it to it become red-hot. This should be tried.

32. If a burning substance is porous, so that the fire in it has room to move, the fire is immediately extinguished if its motion is checked by strong compression. For example, you can immediately extinguish the burning wick of a candle or lamp by snuffing it out with an extinguisher, or burning charcoal or coal by grinding it down with your foot.

33. The closer something is to a hot body the more heat it gets from it; and this applies to light as well—the nearer an object is to a light-source the more visible it becomes.

34. Combining different heats increases the ·over-all· heat unless the combining is done by mixing the hot substances together. For a large fire and a small fire in the same house give more heat than either alone, but warm water poured into boiling water cools it.

35. The longer a hot body is applied to something else,the more heat it gives it; because heat is perpetually being transferred and mixed in with the heat that is already there, so that amount of heat transferred increases through time. A fire doesn’t warm a room as well in half an hour as it does if continued through a whole hour. Not so with light: a lamp or candle gives no more light after it has been long lighted than it did at first.

36. Irritation by surrounding cold increases heat, as you can see in fires during a sharp frost. I think this is not so much because the cold confines and contracts the heat. . . .as because it irritates it. ·Another example of such irritation—one that doesn’t concern heat—occurs· when air is forcefully compressed or a stick is forcefully bent; it doesn’t merely rebound back to its initial position but goes further than that. A careful experiment is needed here: put a stick or some such thing into a flame, and see whether it isn’t burned more quickly at the edge of the flame than at its centre.

37. Things differ greatly in how susceptible to heat they are. Note first of all how even the bodies that are least susceptible of heat are warmed a little by faint heat. Even a piece of metal warms up a little if held for a while in your hand. So readily and universally is heat transmitted and aroused—without the warmed body changing its appearance.

Item 38: How to Make a Thermometer

38. Of all the substances we know, the one that gets and gives heat most readily is air. You can see this in calendar glasses [ = ‘thermometers’], which are made thus.

•Take a glass flask with a rounded belly and a narrow elongated neck;
•attach along its neck a strip of paper marked with as many degrees as you choose;
•use a flame to warm the flask’s belly; then
•turn the flask upside down and lower it—mouth down and belly up—into another glass vessel containing water. Let the mouth of the inserted flask touch the bottom of the receiving vessel, with the flask’s neck resting lightly on the mouth of the receiving vessel. (It may help if you apply a little wax to the mouth of the receiving vessel, but not so as to create a seal. We are going to be dealing with very light and delicate movements, and we don’t want them to be blocked because air can’t pass through.

·There is your equipment; and now here is the experiment·. The air in the flask was expanded by the heat of the flame; and now it will contract as the flask cools down, so that eventually the flask will contain the same amount of air as before but in a smaller space than that of the entire flask. The remaining space in the flask will be filled with water from the receiving vessel. You’ll see that the colder the day is the more the air contracts and thus the more water is drawn up into the flask; and the markings on the flask’s neck will let you measure these changes. Air is much more finely sensitive to heat and cold than we are with our sense of touch; a ray of sunshine, or the heat of your breath, not to mention the heat of your hand placed on the top of the glass, will lower the level of the water by a perceptible amount. Yet I think that animal spirits are even more sensitive to heat and cold, or would be if they weren’t deadened by the mass of the body.

39. Next to air, the bodies that seem to me most sensitive to heat are ones that have recently been compressed by cold, such as snow and ice; for it takes only a very gentle heat to start them melting. Next, perhaps, comes mercury. Then fatty substances such as oil, butter, etc.; then wood; then water; and lastly stones and metals, which are slow to heat, especially internally. These ·slow-to-heat substances·, however, once they are hot, remain so for a long time; so much so that when an intensely hot brick, stone or piece of iron is plunged into a basin of water it remains too hot to touch for nearly a quarter of an hour.

40. The less mass a body has the more quickly it grows warm from being near a hot body; which shows that all heat in our experience is in some way opposed to tangible matter.

41. To the human sense of touch, heat is a variable and relative thing; tepid water feels hot to a hand that was cold, and cold to a hand that was hot.

14. From the above tables you can see how impoverished my ·natural· history is. I have ·frequently· offered, in place of proven history and solid instances, mere traditions and hearsay. I have always noted the doubtful credibility and authority of these, ·but that doesn’t alter the fact that they represent gaps in my natural history, which is why· I have often had to resort to saying things like ‘Try an experiment’ and ‘We should inquire’.

The next post in the sequence will be posted Thursday, November 7 at latest by 4:00pm PT.