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instance destroys an 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, &c.) 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 redhot iron and the flame of spirits of wine, (for the iron is more hot and less bright, whilst 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,* 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

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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 tables. are merely offering examples, and not perfect

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

Aph. 19.

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 farther, 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.

20. 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 any thing 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* 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 the 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 sensations) 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 healing 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 assist ance; 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 vapour is clearly dilated and bursts into flame.

"Quid ipsum," the rò ri hv elva of Aristotle. VOL. III.-49

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 farther, 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; 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 towards the exterior, but at the same time bearing the body upwards. 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 upwards.

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

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nature of cold; whether its contraction be down- | is very slow, and attacks very minute particles, wards, as the expansion of heat is upwards. no heat is perceived. 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 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 almost 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

It is also shown by the fires burning most exert itself in the smaller particles." The expanbriskly in the coldest weather.

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sion is modified by its tendency to rise though expanding towards the exterior;" and the effort is modified by its not being sluggish, but active and somewhat violent.

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, al- With regard to the operative definition, the though they break out very violently, no remark-matter is the same. "If you are able to excite a able 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 needlepoints. 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 inwards or outwards, 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.

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.

21. 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 doc. trine.

It is shown by comparing the effects of fire In the first place, therefore, we will treat of with those of time. Time dries, consumes, under-prerogative instances; 2. Of the supports of inmines, and reduces to ashes as well as fire, and, perhaps, to a much finer degree, but as its motion

duction; 3. Of the correction of induction; 4. Of varying the investigation according to the nature

of the subject; 5. Of the prerogative natures with | And, although all exclusion advances affirmation, respect to investigation, or of what should be the yet this takes place more directly in the same 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.

22. Amongst 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 colour: Prisms, crystalline gems, which yield colours not only internally but on the wall, dews, &c., are solitary instances. For they have nothing in common with the fixed colours in flowers and coloured gems, metals, woods, &c., except the colour itself. Hence we easily deduce that colour 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.* These are solitary instances as regards similitude.

Again, in the same inquiry, the distinct veins of white and black in marble, and the variegated colours 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 colour. Thence we easily deduce that colour 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.

than in different subjects. But, if the form (15 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 towards 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 towards 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 transparen

23. In the second rank of prerogative instances we will consider Migrating instances. In these, the required nature passes towards generation, having no previous existence, or towards 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 Dassage, and then brought to the opposite conclu-cy, those which are uneven and of simple texture, sion. 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.

This very nearly approaches to Sir I. Newton's discovery the decomposition of light by the prism.

whiteness, those which are uneven and of compound but regular texture, all the other colours 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 towards generation in the required nature of whiteness. An instance

migrating towards 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 towards generation and destruction, but also those which pass towards 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. 24. 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 vigour 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 exhibit expansion, yet, from its being extinguished every moment, it des not exhibit the progress of expansion. Boiling water, again, from its rapid conversion into vapour, does not so well exhibit the expansion of water in its own shape: whilst red-hot ion, 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 articles which subdue and restrain it. But the thermometer strikingly exhibits the expansion of the air, as being evident and progressive, durable, and not transitory.

Take another example. Let the required nature be weight. Quicksilver is a conspicuous instance of weight; for it is far heavier than any other substance except gold, which is not much heavier;

and it is a better instance than gold for the purpose of indicating the form of weight. For gold is solid and consistent, which qualities must be referred to density, but quicksilver is liquid, and teeming with spirit, yet much heavier than the diamond and other substances considered to be most solid. Whence it is shown that the form of gravity or weight predominates only in the quantity of matter, and not in the close fitting of it.

25. In the fourth rank of prerogative instances we will class clandestine instances; which we are also wont to call twilight instances. They are, as it were, opposed to the conspicuous instances; for they show the required nature in its lowest state of efficacy, and, as it were, its cradle and first rudiments, making an effort, and a sort of first attempt, but concealed and subdued by a contrary nature. Such instances are, however, of great importance in discovering forms, for, as the conspicuous tend easily to differences, so do the clandestine best lead to genera; that is, to those common natures of which the required natures are only the limits.

As an example: let consistency, or that which confines itself, be the required nature, the opposite of which is a liquid or flowing state. The clandestine instances are such as exhibit some weak and low degree of consistency in fluids, as a water bubble, which is a sort of consistent and bounded pellicle, formed out of the substance of the water. So eaves' droppings, if there be enough water to follow them, draw themselves out into a thin thread, not to break the continuity of the water, but if there be not enough to follow, the water forms itself into a round drop, which is the best form to prevent a breach of continuity: and at the moment the thread ceases, and the water begins to fall in drops, the thread of water recoils upwards to avoid such a breach. Nay, in metals, which, when melted, are liquid, but more tenacious, the melted drops often recoil and are suspended. There is something similar in the instance of the child's looking-glass, which little boys will sometimes form of spittle between rushes, and where the same pellicle of water is observable: and still more in that other amusement of children, when they take some water rendered a little more tenacious by soap, and inflate it with a pipe, forming the water into a sort of castle of bubbles, which assumes such consistency by the interposition of the air, as to admit of being thrown some little distance without bursting. The best example is that of froth and snow, which assume such consistency as almost to admit of being cut, although composed of air and water, both liquids. All these circumstances clearly show that the terms liquid and consistent are merely vulgar notions adapted to the sense, and that in reality all bodies have a tendency to avoid a breach of continuity, faint

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