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in which respect I have observed, that if a glass be placed at the distance of ten inches, for instance, from the combustible object, it does not kindle or burn it so readily, as if the glass be placed at the distance of five inches (for instance), and be then gradually and slowly withdrawn to the distance of ten inches. The cone and focus of the rays, however, are the same, but the mere motion increases the effect of the heat.
29. Conflagrations, which take place with a high wind, are thought to make greater way against than with the wind, because when the wind slackens the flame recoils more rapidly than it advances when the wind is favourable.
30. Flame does not burst out or arise unless it have some hollow space to move and exert itself in, except in the exploding flame of gunpowder, and the like, where the compression and confinement of the flame increase its fury.
31. The anvil becomes so hot by the hammer, that if it were a thin plate it might probably grow red like ignited iron by repeated strokes. Let the experiment be tried.
32. But in ignited bodies that are porous, so as to leave room for the fire to move itself, if its motion be prevented by strong compression, the fire is immediately extinguished ; thus it is with tinder, or the burning snuff of a candle or lamp, or even hot charcoal or cinders, for when they are squeezed by snuffers, or the foot, and the like, the effect of the fire instantly ceases.
33. The approach towards a hot body increases heat in proportion to the approximation; a similar effect to that of light, for the nearer any object is placed towards the light, the more visible it becomes.
34. The union of different heats increases heat, unless the substances be mixed. For a large and small fire in the same spot tend mutually to increase each other's heat, but lukewarm water poured into boiling water cools it.
35. The continued neighbourhood of a warm body increases heat. For the heat, which perpetually passes and emanates from it, being mixed with that which preceded it, multiplies the whole. A fire, for instance, does not warm a room in half an hour, as much as the same fire would in an hour. This does not apply to light, for a lamp or candle placed in any spot gives no more light by remaining there, than it did at first.
*The fires supply fresh heat, the water has only a certain quantity of heat, which being diffused over a fresh supply of cooler water must be on the whole lowered.
36. The irritation of surrounding cold increases heat, as may be seen in fires during a sharp frost. We think that this is owing not merely to the confinement and compression of the heat (which forms a sort of union); but also by the exasperation of it, as when the air or a stick are violently compressed or bent, they recoil, not only to the point they first occupied, but still further back. Let an accurate experiment, therefore, be made with a stick, or something of the kind, put into the flame, in order to see whether it be not sooner burnt at the sides than in the middle of it.*
37. There are many degrees in the susceptibility of heat. And, first, it must be observed how much a low gentle heat changes and partially warms even the bodies least susceptible of it. For even the heat of the hand imparts a little warmth to a ball of lead or other metal held a short time in it. So easily is heat transmitted and excited, without any apparent change in the body.
38. Of all bodies that we are acquainted with, air admits and loses heat the most readily, which is admirably seen in weather-glasses, whose construction is as follows. Take a glass with a hollow belly, and a thin and long neck; turn it upside down, and place it with its mouth downwards into another glass vessel containing water; the end of the tube touching the bottom of the vessel, and the tube itself leaning a little on the edge, so as to be fixed upright. In order to do this more readily, let a little wax be applied to the edge, not however so as to block up the orifice, lest by preventing the air from escaping, the motion, which we shall presently speak of, and which is very gentle and delicate, should be impeded.
Before the first glass be inserted in the other, its upper part (the belly) should be warmed at the fire. Then upon placing it as we have described, the air (which was dilated by the heat), after a sufficient time has been allowed for it to lose the additional temperature, will restore and contract itself to the same dimensions as that of the external or common atmosphere at the moment of immersion, and the water will be attracted upwards in the tube to a proportionate extent. A long narrow slip of paper should be attached to the tube, divided into as many degrees as you
If condensation were the cause of the greater heat, Bacon concludes the centre of the flame would be the hotter part, and vice versa. The fact is, neither of the causes assigned by Bacon is the true one; for the fire burns more quickly only because the draught of air is more rapid, the cold dense air pressing rapidly into the heated room and towards the chimney.
please. You will then perceive, as the weather grows warmer or colder, that the air contracts itself into a narrower space in cold weather and dilates in the warm, which will be exhibited by the rising of the water as the air contracts itself, and its depression as the air dilates. The sensibility of the air with regard to heat or cold is so delicate and exquisite, that it far exceeds the human touch, so that a ray of sunshine, the heat of the breath, and much more, that of the hand placed on the top of the tube, immediately causes an evident depression of the water. We think, however, that the spirit of animals possesses a much more delicate susceptibility of heat and cold, only that it is impeded and blunted by the grossness of their bodies.
39. After air we consider those bodies to be most sensible of heat, which have been recently changed and contracted by cold, as snow and ice; for they begin to be dissolved and melt with the first mild weather. Next, perhaps, follows quicksilver; then greasy substances, as oil, butter, and the like; then wood; then water; lastly, stones and metals, which do not easily grow hot, particularly towards their centre. When heated, however, they retain their temperature for a very long time; so that a brick or stone, or hot iron, plunged in a basin of cold water, and kept there for a quarter of an hour or thereabouts, retains such a heat as not to admit of being touched.
40. The less massive the body is, the more readily it grows warm at the approach of a heated body, which shows that heat with us is somewhat averse to a tangible mass.†
41. Heat with regard to the human senses and touch is various and relative, so that lukewarm water appears hot if the hand be cold, and cold if the hand be hot.
Any one may readily see how poor we are in history, since in the above tables, besides occasionally inserting traditions and report instead of approved history and au
* Bacon appears to have confounded combustibility and fusibility with susceptibility of heat; for though the metals will certainly neither dissolve as soon as ice or butter, nor be consumed as soon as wood, that only shows that different degrees of heat are required to produce similar effects on different bodies; but metals much more readily acquire and transmit the same degree of heat than any of the above substances. The rapid transmission renders them generally cold to the touch. The convenience of fixing wooden handles to vessels containing hot water illustrates these observations.
+ Another singular error, the truth being that solid bodies are the best conductors; but of course where heat is diffused over a large mass, it is less in each part, than if that part also alone received the whole quantum of heat.
thentic instances (always, however, adding some note if their credit or authority be doubtful), we are often forced to subjoin "Let the experiment be tried."-"Let further inquiry be made."
15. We are wont to term the office and use of these three tables the presenting a review of instances to the understanding; and when this has been done induction itself is to be brought into action. For on an individual review of all the instances a nature is to be found, such as always to be present and absent with the given nature, to increase and decrease with it, and as we have said to form a more common limit of the nature. If the mind attempt this affirmatively from the first (which it always will when left to itself), there will spring up phantoms, mere theories and ill defined notions, with axioms requiring daily correction. These will doubtless be better or worse according to the power and strength of the understanding which creates them. But it is only for God (the bestower and creator of forms), and perhaps for angels and intelligences, at once to recognise forms affirmatively at the first glance of contemplation: man at least is unable to do so, and is only allowed to proceed first by negatives, and then to conclude with affirmatives, after every species of exclusion.
16. We must therefore effect a complete solution and separation of nature; not by fire, but by the mind, that divine fire. The first work of legitimate induction, in the discovery of forms, is rejection, or the exclusive instances of individual natures, which are not found in some one instance where the given nature is present, or are found in any one instance where it is absent, or are found to increase in any one instance where the given nature decreases or the reverse. After an exclusion correctly effected, an affirmative form will remain as the residuum, solid, true, and well defined, whilst all volatile opinions go off in smoke. This is readily said, but we must arrive at it by a circuitous route. We shall perhaps, however, omit nothing that can facilitate our progress.
17. The first and almost perpetual precaution and warning which we consider necessary is this: that none should suppose from the great part assigned by us to forms, that we mean such forms as the meditations and thoughts of men have hitherto been accustomed to. In the first place we do not at present mean the concrete forms, which (as we have observed) are in the common course of things compounded of simple natures, as those of a lion, an eagle, a rose, gold, or the like. The moment for discussing these
will arrive when we come to treat of the latent process, and latent conformation, and the discovery of them as they exist in what are called substances, or concrete natures.
Nor again would we be thought to mean (even when treating of simple natures) any abstract forms or ideas, either undefined or badly defined in matter. For when we speak of forms, we mean nothing else than those laws and regulations of simple action which arrange and constitute any simple nature, such as heat, light, weight, in every species of matter and in a susceptible subject. The form of heat or form of light, therefore, means no more than the law of heat, or the law of light. Nor do we ever abstract or withdraw ourselves from things, and the operative branch of philosophy When therefore we say (for instance) in our investigation of the form of heat, reject rarity, or rarity is not of the form of heat, it is the same as if we were to say, "Man can superinduce heat on a dense body," or the reverse, Man can abstract or ward off heat from a rare body."
But if our forms appear to any one to be somewhat abstracted, from their mingling and uniting heterogeneous objects (the heat for instance of the heavenly bodies appears to be very different from that of fire; the fixed red of the rose and the like, from that which is apparent in the rainbow, or the radiation of opal or the diamond ;* death by drowning, from that by burning, the sword, apoplexy, or consumption; and yet they all agree in the common natures of heat, redness, and death), let him be assured that his understanding is enthralled by habit, by general appearances and hypotheses. For it is most certain that, however heterogeneous and distinct, they agree in the form or law which regulates heat, redness, or death; and that human power cannot be emancipated and freed from the common course of nature, and expanded and exalted to new efficients and new modes of operation, except by the revelation and invention of forms of this nature. But after this union of nature, which is the principal point, we will afterwards, in its proper place, treat of the divisions and ramifications of nature, whether ordinary or internal and more real.
18. We must now offer an example of the exclusion or
*This general law or form has been well illustrated by Newton's discovery of the decomposition of colours.
ti. e. the common link or form which connects the various kinds of natures, such as the different hot or red natures enumerated above. See Aphorism 3, Part 2.