The Chemical History of a Candle: Lecture I
蜡烛的化学史：第一讲
迈克尔·法拉第 Michael Faraday（1791–1867）
1860–61 年圣诞讲座，1861 年出版

冷冻图书馆 · 开架书库 · S-006013 · https://coldlibrary.com/s/006013
权利：1860–61 年讲演，1861 年出版；法拉第卒于 1867 年，编者克鲁克斯卒于 1919 年。已按澳大利亚、欧盟、英国、中国大陆和美国的规则核对（截至 2026 年 10 月 11 日）。仅供参考，不是法律意见。
来源：Project Gutenberg，https://www.gutenberg.org/cache/epub/14474/pg14474.txt（取于 2026-10-11）
中文译文：Claude（AI），2026 · CC0 1.0
生成于 2026-10-14，来自 https://coldlibrary.com/open-stacks/faraday-candle-lecture-one

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Lecture I. A Candle: The Flame—Its Sources—Structure—Mobility—Brightness

I purpose, in return for the honour you do us by coming to see what are our proceedings here, to bring before you, in the course of these lectures, the Chemical History of a Candle. I have taken this subject on a former occasion; and were it left to my own will, I should prefer to repeat it almost every year—so abundant is the interest that attaches itself to the subject, so wonderful are the varieties of outlet which it offers into the various departments of philosophy. There is not a law under which any part of this universe is governed which does not come into play, and is touched upon in these phenomena. There is no better, there is no more open door by which you can enter into the study of natural philosophy, than by considering the physical phenomena of a candle. I trust, therefore, I shall not disappoint you in choosing this for my subject rather than any newer topic, which could not be better, were it even so good.

And before proceeding, let me say this also—that though our subject be so great, and our intention that of treating it honestly, seriously, and philosophically, yet I mean to pass away from all those who are seniors amongst us. I claim the privilege of speaking to juveniles as a juvenile myself. I have done so on former occasions—and, if you please, I shall do so again. And though I stand here with the knowledge of having the words I utter given to the world, yet that shall not deter me from speaking in the same familiar way to those whom I esteem nearest to me on this occasion.

And now, my boys and girls, I must first tell you of what candles are made. Some are great curiosities. I have here some bits of timber, branches of trees particularly famous for their burning. And here you see a piece of that very curious substance taken out of some of the bogs in Ireland, called *candle-wood*,—a hard, strong, excellent wood, evidently fitted for good work as a resister of force, and yet withal burning so well that where it is found they make splinters of it, and torches, since it burns like a candle, and gives a very good light indeed. And in this wood we have one of the most beautiful illustrations of the general nature of a candle that I can possibly give. The fuel provided, the means of bringing that fuel to the place of chemical action, the regular and gradual supply of air to that place of action—heat and light—all produced by a little piece of wood of this kind, forming, in fact, a natural candle.

But we must speak of candles as they are in commerce. Here are a couple of candles commonly called dips. They are made of lengths of cotton cut off, hung up by a loop, dipped into melted tallow, taken out again and cooled, then re-dipped until there is an accumulation of tallow round the cotton. In order that you may have an idea of the various characters of these candles, you see these which I hold in my hand—they are very small, and very curious. They are, or were, the candles used by the miners in coal mines. In olden times the miner had to find his own candles; and it was supposed that a small candle would not so soon set fire to the fire-damp in the coal mines as a large one; and for that reason, as well as for economy’s sake, he had candles made of this sort—20, 30, 40, or 60 to the pound. They have been replaced since then by the steel-mill, and then by the Davy-lamp, and other safety-lamps of various kinds. I have here a candle that was taken out of the *Royal George*, it is said, by Colonel Pasley. It has been sunk in the sea for many years, subject to the action of salt water. It shews you how well candles may be preserved; for though it is cracked about and broken a good deal, yet, when lighted, it goes on burning regularly, and the tallow resumes its natural condition as soon as it is fused.

Mr. Field, of Lambeth, has supplied me abundantly with beautiful illustrations of the candle and its materials. I shall therefore now refer to them. And, first, there is the suet—the fat of the ox—Russian tallow, I believe, employed in the manufacture of these dips, which Gay Lussac, or some one who entrusted him with his knowledge, converted into that beautiful substance, stearin, which you see lying beside it. A candle, you know, is not now a greasy thing like an ordinary tallow candle, but a clean thing, and you may almost scrape off and pulverise the drops which fall from it without soiling anything. This is the process he adopted:—The fat or tallow is first boiled with quick-lime, and made into a soap, and then the soap is decomposed by sulphuric acid, which takes away the lime, and leaves the fat re-arranged as stearic acid, whilst a quantity of glycerin is produced at the same time. Glycerin—absolutely a sugar, or a substance similar to sugar—comes out of the tallow in this chemical change. The oil is then pressed out of it; and you see here this series of pressed cakes, shewing how beautifully the impurities are carried out by the oily part as the pressure goes on increasing, and at last you have left that substance which is melted, and cast into candles as here represented. The candle I have in my hand is a stearin candle, made of stearin from tallow in the way I have told you. Then here is a sperm candle, which comes from the purified oil of the spermaceti whale. Here also are yellow bees-wax and refined bees-wax, from which candles are made. Here, too, is that curious substance called paraffin, and some paraffin candles made of paraffin obtained from the bogs of Ireland. I have here also a substance brought from Japan, since we have forced an entrance into that out-of-the-way place—a sort of wax which a kind friend has sent me, and which forms a new material for the manufacture of candles.

And how are these candles made? I have told you about dips, and I will shew you how moulds are made. Let us imagine any of these candles to be made of materials which can be cast. “Cast!” you say. “Why, a candle is a thing that melts; and surely if you can melt it, you can cast it.” Not so. It is wonderful, in the progress of manufacture, and in the consideration of the means best fitted to produce the required result, how things turn up which one would not expect beforehand. Candles cannot always be cast. A wax candle can never be cast. It is made by a particular process, which I can illustrate in a minute or two: but I must not spend much time on it. Wax is a thing which, burning so well, and melting so easily in a candle, cannot be cast. However, let us take a material that can be cast. Here is a frame, with a number of moulds fastened in it. The first thing to be done is to put a wick through them. Here is one—a plaited wick, which does not require snuffing—supported by a little wire. It goes to the bottom, where it is pegged in—the little peg holding the cotton tight, and stopping the aperture, so that nothing fluid shall run out. At the upper part there is a little bar placed across, which stretches the cotton and holds it in the mould. The tallow is then melted, and the moulds are filled. After a certain time, when the moulds are cool, the excess of tallow is poured off at one corner, and then cleaned off altogether, and the ends of the wick cut away. The candles alone then remain in the mould, and you have only to upset them, as I am doing, when out they tumble, for the candles are made in the form of cones, being narrower at the top than at the bottom; so that what with their form and their own shrinking, they only need a little shaking, and out they fall. In the same way are made these candles of stearin and of paraffin. It is a curious thing to see how wax candles are made. A lot of cottons are hung upon frames, as you see here, and covered with metal tags at the ends to keep the wax from covering the cotton in those places. These are carried to a heater, where the wax is melted. As you see, the frames can turn round; and as they turn, a man takes a vessel of wax and pours it first down one, and then the next and the next, and so on. When he has gone once round, if it is sufficiently cool, he gives the first a second coat, and so on until they are all of the required thickness. When they have been thus clothed, or fed, or made up to that thickness, they are taken off, and placed elsewhere. I have here, by the kindness of Mr. Field, several specimens of these candles. Here is one only half-finished. They are then taken down, and well rolled upon a fine stone slab, and the conical top is moulded by properly shaped tubes, and the bottoms cut off and trimmed. This is done so beautifully that they can make candles in this way weighing exactly four, or six, to the pound, or any number they please.

We must not, however, take up more time about the mere manufacture, but go a little further into the matter. I have not yet referred you to luxuries in candles (for there is such a thing as luxury in candles). See how beautifully these are coloured: you see here mauve, magenta, and all the chemical colours recently introduced, applied to candles. You observe, also, different forms employed. Here is a fluted pillar most beautifully shaped; and I have also here some candles sent me by Mr. Pearsall, which are ornamented with designs upon them, so that as they burn you have as it were a glowing sun above, and a bouquet of flowers beneath. All, however, that is fine and beautiful is not useful. These fluted candles, pretty as they are, are bad candles; they are bad because of their external shape. Nevertheless, I shew you these specimens sent to me from kind friends on all sides, that you may see what is done, and what may be done in this or that direction; although, as I have said, when we come to these refinements, we are obliged to sacrifice a little in utility.

Now, as to the light of the candle. We will light one or two, and set them at work in the performance of their proper functions. You observe a candle is a very different thing from a lamp. With a lamp you take a little oil, fill your vessel, put in a little moss or some cotton prepared by artificial means, and then light the top of the wick. When the flame runs down the cotton to the oil, it gets extinguished, but it goes on burning in the part above. Now, I have no doubt you will ask, how is it that the oil, which will not burn of itself, gets up to the top of the cotton, where it will burn? We shall presently examine that; but there is a much more wonderful thing about the burning of a candle than this. You have here a solid substance with no vessel to contain it; and how is it that this solid substance can get up to the place where the flame is? How is it that this solid gets there, it not being a fluid? or, when it is made a fluid, then how is it that it keeps together? This is a wonderful thing about a candle.

We have here a good deal of wind, which will help us in some of our illustrations, but tease us in others; for the sake, therefore, of a little regularity, and to simplify the matter, I shall make a quiet flame—for who can study a subject when there are difficulties in the way not belonging to it? Here is a clever invention of some costermonger or street stander in the market-place for the shading of their candles on Saturday nights, when they are selling their greens, or potatoes, or fish. I have very often admired it. They put a lamp-glass round the candle, supported on a kind of gallery, which clasps it, and it can be slipped up and down as required. By the use of this lamp-glass, employed in the same way, you have a steady flame, which you can look at, and carefully examine, as I hope you will do, at home.

You see, then, in the first instance, that a beautiful cup is formed. As the air comes to the candle it moves upwards by the force of the current which the heat of the candle produces, and it so cools all the sides of the wax, tallow, or fuel, as to keep the edge much cooler than the part within; the part within melts by the flame that runs down the wick as far as it can go before it is extinguished, but the part on the outside does not melt. If I made a current in one direction, my cup would be lop-sided, and the fluid would consequently run over,—for the same force of gravity which holds worlds together holds this fluid in a horizontal position, and if the cup be not horizontal, of course the fluid will run away in guttering. You see, therefore, that the cup is formed by this beautifully regular ascending current of air playing upon all sides, which keeps the exterior of the candle cool. No fuel would serve for a candle which has not the property of giving this cup, except such fuel as the Irish bogwood, where the material itself is like a sponge, and holds its own fuel. You see now why you would have had such a bad result if you were to burn these beautiful candles that I have shewn you, which are irregular, intermittent in their shape, and cannot therefore have that nicely-formed edge to the cup which is the great beauty in a candle. I hope you will now see that the perfection of a process—that is, its utility—is the better point of beauty about it. It is not the best looking thing, but the best acting thing, which is the most advantageous to us. This good-looking candle is a bad burning one. There will be a guttering round about it because of the irregularity of the stream of air and the badness of the cup which is formed thereby. You may see some pretty examples (and I trust you will notice these instances) of the action of the ascending current when you have a little gutter run down the side of a candle, making it thicker there than it is elsewhere. As the candle goes on burning, that keeps its place and forms a little pillar sticking up by the side, because, as it rises higher above the rest of the wax or fuel, the air gets better round it, and it is more cooled and better able to resist the action of the heat at a little distance. Now, the greatest mistakes and faults with regard to candles, as in many other things, often bring with them instruction which we should not receive if they had not occurred. We come here to be philosophers; and I hope you will always remember that whenever a result happens, especially if it be new, you should say, “What is the cause? Why does it occur?” and you will in the course of time find out the reason.

Then, there is another point about these candles which will answer a question,—that is, as to the way in which this fluid gets out of the cup, up the wick, and into the place of combustion. You know that the flames on these burning wicks in candles made of bees-wax, stearin, or spermaceti, do not run down to the wax or other matter, and melt it all away, but keep to their own right place. They are fenced off from the fluid below, and do not encroach on the cup at the sides. I cannot imagine a more beautiful example than the condition of adjustment under which a candle makes one part subserve to the other to the very end of its action. A combustible thing like that, burning away gradually, never being intruded upon by the flame, is a very beautiful sight; especially when you come to learn what a vigorous thing flame is—what power it has of destroying the wax itself when it gets hold of it, and of disturbing its proper form if it come only too near.

But how does the flame get hold of the fuel? There is a beautiful point about that—*capillary attraction*. “Capillary attraction!” you say,—“the attraction of hairs.” Well, never mind the name: it was given in old times, before we had a good understanding of what the real power was. It is by what is called capillary attraction that the fuel is conveyed to the part where combustion goes on, and is deposited there, not in a careless way, but very beautifully in the very midst of the centre of action which takes place around it. Now, I am going to give you one or two instances of capillary attraction. It is that kind of action or attraction which makes two things that do not dissolve in each other still hold together. When you wash your hands, you wet them thoroughly; you take a little soap to make the adhesion better, and you find your hand remains wet. This is by that kind of attraction of which I am about to speak. And, what is more, if your hands are not soiled (as they almost always are by the usages of life), if you put your finger into a little warm water, the water will creep a little way up the finger, though you may not stop to examine it. I have here a substance which is rather porous—a column of salt—and I will pour into the plate at the bottom, not water, as it appears, but a saturated solution of salt which cannot absorb more; so that the action which you see will not be due to its dissolving anything. We may consider the plate to be the candle, and the salt the wick, and this solution the melted tallow. (I have coloured the fluid, that you may see the action better.) You observe that, now I pour in the fluid, it rises and gradually creeps up the salt higher and higher; and provided the column does not tumble over, it will go to the top.

If this blue solution were combustible, and we were to place a wick at the top of the salt, it would burn as it entered into the wick. It is a most curious thing to see this kind of action taking place, and to observe how singular some of the circumstances are about it. When you wash your hands, you take a towel to wipe off the water; and it is by that kind of wetting, or that kind of attraction which makes the towel become wet with water, that the wick is made wet with the tallow. I have known some careless boys and girls (indeed, I have known it happen to careful people as well) who, having washed their hands and wiped them with a towel, have thrown the towel over the side of the basin, and before long it has drawn all the water out of the basin and conveyed it to the floor, because it happened to be thrown over the side in such a way as to serve the purpose of a syphon. That you may the better see the way in which the substances act one upon another, I have here a vessel made of wire gauze filled with water, and you may compare it in its action to the cotton in one respect, or to a piece of calico in the other. In fact, wicks are sometimes made of a kind of wire gauze. You will observe that this vessel is a porous thing; for if I pour a little water on to the top, it will run out at the bottom. You would be puzzled for a good while if I asked you what the state of this vessel is, what is inside it, and why it is there? The vessel is full of water, and yet you see the water goes in and runs out as if it were empty. In order to prove this to you, I have only to empty it. The reason is this,—the wire, being once wetted, remains wet; the meshes are so small that the fluid is attracted so strongly from the one side to the other, as to remain in the vessel although it is porous. In like manner the particles of melted tallow ascend the cotton and get to the top; other particles then follow by their mutual attraction for each other, and as they reach the flame they are gradually burned.

Here is another application of the same principle. You see this bit of cane. I have seen boys about the streets, who are very anxious to appear like men, take a piece of cane, and light it and smoke it, as an imitation of a cigar. They are enabled to do so by the permeability of the cane in one direction, and by its capillarity. If I place this piece of cane on a plate containing some camphine (which is very much like paraffin in its general character), exactly in the same manner as the blue fluid rose through the salt will this fluid rise through the piece of cane. There being no pores at the side, the fluid cannot go in that direction, but must pass through its length. Already the fluid is at the top of the cane: now I can light it and make it serve as a candle. The fluid has risen by the capillary attraction of the piece of cane, just as it does through the cotton in the candle.

Now, the only reason why the candle does not burn all down the side of the wick is, that the melted tallow extinguishes the flame. You know that a candle, if turned upside-down, so as to allow the fuel to run upon the wick, will be put out. The reason is, that the flame has not had time to make the fuel hot enough to burn, as it does above, where it is carried in small quantities into the wick, and has all the effect of the heat exercised upon it.

There is another condition which you must learn as regards the candle, without which you would not be able fully to understand the philosophy of it, and that is the vaporous condition of the fuel. In order that you may understand that, let me shew you a very pretty, but very common-place experiment. If you blow a candle out cleverly, you will see the vapour rise from it. You have, I know, often smelt the vapour of a blown-out candle—and a very bad smell it is; but if you blow it out cleverly, you will be able to see pretty well the vapour into which this solid matter is transformed. I will blow out one of these candles in such a way as not to disturb the air around it, by the continuing action of my breath; and now, if I hold a lighted taper two or three inches from the wick, you will observe a train of fire going through the air till it reaches the candle. I am obliged to be quick and ready, because, if I allow the vapour time to cool, it becomes condensed into a liquid or solid, or the stream of combustible matter gets disturbed.

Now, as to the shape or form of the flame. It concerns us much to know about the condition which the matter of the candle finally assumes at the top of the wick—where you have such beauty and brightness as nothing but combustion or flame can produce.

You have the glittering beauty of gold and silver, and the still higher lustre of jewels, like the ruby and diamond; but none of these rival the brilliancy and beauty of flame. What diamond can shine like flame? It owes its lustre at night-time to the very flame shining upon it. The flame shines in darkness, but the light which the diamond has is as nothing until the flame shine upon it, when it is brilliant again. The candle alone shines by itself, and for itself, or for those who have arranged the materials. Now, let us look a little at the form of the flame as you see it under the glass shade. It is steady and equal; and its general form is that which is represented in the diagram, varying with atmospheric disturbances, and also varying according to the size of the candle. It is a bright oblong—brighter at the top than towards the bottom—with the wick in the middle, and besides the wick in the middle, certain darker parts towards the bottom, where the ignition is not so perfect as in the part above.

I have a drawing here, sketched many years ago by Hooke, when he made his investigations. It is the drawing of the flame of a lamp, but it will apply to the flame of a candle. The cup of the candle is the vessel or lamp, the melted spermaceti is the oil, and the wick is common to both. Upon that he sets this little flame, and then he represents what is true—a certain quantity of matter rising about it which you do not see, and which, if you have not been here before, or are not familiar with the subject, you will not know of. He has here represented the parts of the surrounding atmosphere that are very essential to the flame, and that are always present with it. There is a current formed, which draws the flame out—for the flame which you see is really drawn out by the current, and drawn upward to a great height—just as Hooke has here shewn you by that prolongation of the current in the diagram. You may see this by taking a lighted candle, and putting it in the sun so as to get its shadow thrown on a piece of paper. How remarkable it is that that thing which is light enough to produce shadows of other objects, can be made to throw its own shadow on a piece of white paper or card, so that you can actually see streaming round the flame something which is not part of the flame, but is ascending and drawing the flame upwards. Now, I am going to imitate the sunlight, by applying the voltaic battery to the electric lamp. You now see our sun, and its great luminosity; and by placing a candle between it and the screen, we get the shadow of the flame.

You observe the shadow of the candle and of the wick; then there is a darkish part, as represented in the diagram, and then a part which is more distinct. Curiously enough, however, what we see in the shadow as the darkest part of the flame is, in reality, the brightest part; and here you see streaming upwards the ascending current of hot air, as shewn by Hooke, which draws out the flame, supplies it with air, and cools the sides of the cup of melted fuel.

I can give you here a little further illustration, for the purpose of shewing you how flame goes up or down; according to the current. I have here a flame—it is not a candle-flame—but you can, no doubt, by this time, generalise enough to be able to compare one thing with another. What I am about to do is to change the ascending current that takes the flame upwards into a descending current. This I can easily do by the little apparatus you see before me. The flame, as I have said, is not a candle flame, but it is produced by alcohol, so that it shall not smoke too much. I will also colour the flame with another substance, so that you may trace its course; for with the spirit alone you could hardly see well enough to have the opportunity of tracing its direction. By lighting this spirit-of-wine, we have then a flame produced; and you observe that when held in the air, it naturally goes upwards.

You understand now easily enough why flames go up under ordinary circumstances—it is because of the draught of air by which the combustion is formed. But now, by blowing the flame down, you see I am enabled to make it go downwards into this little chimney—the direction of the current being changed. Before we have concluded this course of lectures, we shall shew you a lamp in which the flame goes up and the smoke goes down, or the flame goes down and the smoke goes up. You see, then, that we have the power in this way of varying the flame in different directions.

There are now some other points that I must bring before you. Many of the flames you see here vary very much in their shape by the currents of air blowing around them in different directions; but we can, if we like, make flames so that they will look like fixtures, and we can photograph them—indeed, we have to photograph them—so that they become fixed to us, if we wish to find out everything concerning them. That, however, is not the only thing I wish to mention. If I take a flame sufficiently large, it does not keep that homogeneous, that uniform condition of shape, but it breaks out with a power of life which is quite wonderful. I am about to use another kind of fuel, but one which is truly and fairly a representative of the wax or tallow of a candle. I have here a large ball of cotton, which will serve as a wick. And, now that I have immersed it in spirit and applied a light to it, in what way does it differ from an ordinary candle? Why, it differs very much in one respect, that we have a vivacity and power about it, a beauty and a life entirely different from the light presented by a candle. You see those fine tongues of flame rising up. You have the same general disposition of the mass of the flame from below upwards; but, in addition to that, you have this remarkable breaking out into tongues which you do not perceive in the case of a candle. Now, why is this? I must explain it to you, because when you understand that perfectly, you will be able to follow me better in what I have to say hereafter. I suppose some here will have made for themselves the experiment I am going to shew you. Am I right in supposing that anybody here has played at snapdragon? I do not know a more beautiful illustration of the philosophy of flame, as to a certain part of its history, than the game of snapdragon. First, here is the dish; and let me say, that when you play snapdragon properly, you ought to have the dish well-warmed; you ought also to have warm plums and warm brandy, which, however, I have not got. When you have put the spirit into the dish, you have the cup and the fuel; and are not the raisins acting like the wicks? I now throw the plums into the dish, and light the spirit, and you see those beautiful tongues of flame that I refer to. You have the air creeping in over the edge of the dish forming these tongues. Why? Because, through the force of the current and the irregularity of the action of the flame, it cannot flow in one uniform stream. The air flows in so irregularly that you have what would otherwise be a single image, broken up into a variety of forms, and each of these little tongues has an independent existence of its own. Indeed, I might say, you have here a multitude of independent candles. You must not imagine, because you see these tongues all at once, that the flame is of this particular shape. A flame of that shape is never so at any one time. Never is a body of flame, like that which you just saw rising from the ball, of the shape it appears to you. It consists of a multitude of different shapes, succeeding each other so fast that the eye is only able to take cognisance of them all at once. In former times, I purposely analysed a flame of that general character, and the diagram shews you the different parts of which it is composed. They do not occur all at once: it is only because we see these shapes in such rapid succession, that they seem to us to exist all at one time.

It is too bad that we have not got further than my game of snapdragon; but we must not, under any circumstances, keep you beyond your time. It will be a lesson to me in future to hold you more strictly to the philosophy of the thing, than to take up your time so much with these illustrations.


The close of the last lecture

Thus you see the analogy between respiration and combustion is rendered still more beautiful and striking. Indeed, all I can say to you at the end of these lectures (for we must come to an end at one time or other) is to express a wish that you may, in your generation, be fit to compare to a candle; that you may, like it, shine as lights to those about you; that, in all your actions, you may justify the beauty of the taper by making your deeds honourable and effectual in the discharge of your duty to your fellow-men.

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中文译文 · Claude（AI）译

第一讲　一支蜡烛：火焰——它的来源——结构——流动——亮度

承蒙诸位光临，来看看我们在这里做些什么；作为回报，我打算在这几次讲座中，给大家讲一讲“一支蜡烛的化学史”。这个题目我以前讲过；如果由着我自己的心意，我宁愿几乎每年都讲一遍——这个题目里的趣味是那样丰富，它通向自然哲学各个门类的出口又是那样千变万化。支配着这个宇宙任何一部分的法则，没有一条不在这些现象中起作用、不被它们触及。要走进自然哲学的研究，没有比考察一支蜡烛的物理现象更好的门、更敞开的门了。所以我相信，我选了这个题目，而不是什么更新的话题，不会让大家失望；更新的话题即使和它一样好，也不会比它更好。

开讲之前，还有一句话要说：虽然我们的题目这样宏大，我们的本意是要诚实地、严肃地、以哲学的态度来对待它，但我却打算撇开在座的各位长辈。我要求享有这样的特权：作为一个少年，对少年们说话。以前我这样做过——如果诸位允许，我还要这样做。虽然我站在这里，知道我说的话会传到全世界，但这不会妨碍我用同样亲切的方式，对今天我认为离我最近的人们讲话。

那么，孩子们，我首先得告诉你们蜡烛是用什么做的。有些蜡烛是很稀奇的东西。我这里有几块木头，是一些以好烧出名的树的枝条。你们看，这里还有一块从爱尔兰沼泽里挖出来的非常奇特的东西，叫作“烛木”——一种坚硬、结实、极好的木头，显然很适合做需要承受力量的活计，可同时又烧得那么好，在出产它的地方，人们把它劈成细条，做成火把，因为它像蜡烛一样燃烧，发出的光确实很好。在这块木头里，我们有了一个我所能举出的最美的例子，来说明蜡烛的一般性质：备好的燃料，把燃料送到化学作用发生之处的办法，向那个地方有规律地、逐渐地供应空气——热和光——这一切都由这样一小块木头产生，它实际上就是一支天然的蜡烛。

不过我们得说说市面上的蜡烛。这里有两支通常叫作“蘸烛”的蜡烛。它们是这样做的：把棉线剪成一段一段，用一个线圈挂起来，在熔化的牛脂里蘸一下，提出来晾凉，再蘸，直到棉线周围积起一层牛脂。为了让你们对这些蜡烛的各种特点有个概念，请看我手里拿的这几支——它们非常小，也非常稀奇。它们是，或者说曾经是，煤矿里矿工用的蜡烛。从前，矿工得自备蜡烛；人们认为小蜡烛不像大蜡烛那样容易点燃煤矿里的瓦斯，因为这个缘故，也为了节省，矿工就让人做这样的蜡烛——一磅二十支、三十支、四十支或六十支。后来，它们先被钢轮发火器取代，又被戴维灯和其他各种安全灯取代。我这里有一支蜡烛，据说是帕斯利上校从“皇家乔治号”上打捞出来的。它沉在海里许多年，受着海水的侵蚀。它向你们表明蜡烛能保存得多么好；因为它虽然到处开裂、残破不堪，可一点上，还是照常燃烧，牛脂一熔化就恢复了它本来的状态。

兰贝斯的菲尔德先生给了我大量精美的实物，用来说明蜡烛及其材料。我现在就来讲讲它们。首先是板油——牛的脂肪——我想是俄国牛脂，用来制造这些蘸烛；盖-吕萨克，或者某个把自己的知识托付给他的人，把它变成了你们看到的放在它旁边的那种美丽的物质——硬脂。你们知道，如今的蜡烛已不像普通牛脂蜡烛那样油腻腻的，而是干干净净的，从它上面滴下来的蜡滴，你差不多可以刮下来碾成粉，而不会弄脏任何东西。他采用的方法是这样的：先把脂肪或牛脂和生石灰一起煮，制成一种皂，然后用硫酸把这种皂分解，硫酸夺走石灰，留下重新排列成硬脂酸的脂肪，同时还生成一定量的甘油。甘油——简直就是一种糖，或者说一种类似糖的物质——就在这一化学变化中从牛脂里出来了。然后把其中的油压出来；你们看这里这一系列压过的饼块，它们表明，随着压力不断加大，杂质是怎样被油性的部分漂亮地带出来的，最后剩下的就是那种物质，把它熔化，浇铸成这里展示的蜡烛。我手里这支是硬脂蜡烛，是用我刚才说的方法、以牛脂制得的硬脂做的。这里还有一支鲸蜡烛，原料来自抹香鲸提纯的油。这里还有黄蜂蜡和精制蜂蜡，也可以用来做蜡烛。这里还有那种奇特的物质，叫作石蜡，还有几支石蜡蜡烛，用的石蜡是从爱尔兰的沼泽里提取的。我这里还有一种从日本带来的物质——自从我们强行打开了那个偏远之地的门户以来——是一位好心的朋友送给我的一种蜡，它是制造蜡烛的一种新材料。

那么这些蜡烛是怎么做的呢？蘸烛我已经讲过了，现在我给你们看看模子是怎么用的。我们设想这些蜡烛中的任何一种是用可以浇铸的材料做的。“浇铸！”你们会说，“蜡烛是会熔化的东西；既然能熔化，当然就能浇铸。”并非如此。在制造的进程中，在考虑用什么手段最适于得到所需的结果时，常会冒出一些事先意想不到的情况，这真是奇妙。蜡烛并不总是能浇铸的。蜂蜡蜡烛就永远不能浇铸。它是用一种特别的工序做成的，我一两分钟就能说明白，但我不能在这上面花太多时间。蜡这种东西，在蜡烛里烧得那么好，熔化得那么容易，却不能浇铸。不过，我们还是拿一种可以浇铸的材料来说吧。这里有一个架子，上面固定着许多模子。首先要做的，是把烛芯穿过模子。这里就有一根——一根编织的烛芯，不需要剪烛花——由一根细金属丝撑着。它一直通到底部，在那里用小钉子钉住——小钉子把棉芯拉紧，同时堵住小孔，使液体流不出去。在上部，横放着一根小棍，把棉芯绷直，固定在模子里。然后把牛脂熔化，灌满模子。过一段时间，等模子凉了，把多余的牛脂从一角倒掉，再全部清理干净，剪去烛芯的两头。这时模子里就只剩下蜡烛了，你只要把它们倒过来——就像我现在这样——蜡烛就滚出来了；因为蜡烛做成圆锥形，上面比下面细；所以凭着它们的形状，再加上它们自身的收缩，只要稍微摇一摇，它们就掉出来了。这些硬脂蜡烛和石蜡蜡烛也是这样做的。看蜂蜡蜡烛是怎么做的，可是件很有意思的事。把许多根棉芯挂在架子上，就像你们在这里看到的那样，两头套上金属箍，免得那些地方被蜡裹住。把它们搬到加热器旁，那里的蜡已经熔化了。你们看，架子能转动；随着它转动，一个人拿着一罐蜡，先往一根棉芯上浇，然后是下一根，再下一根，依此类推。他转完一圈，如果蜡已经足够凉了，就给第一根浇第二层，如此反复，直到所有的蜡烛都达到所需的粗细。这样穿上了衣裳，或者说喂饱了，长到那样粗了，就把它们取下来，放到别处。承蒙菲尔德先生的好意，我这里有几支这种蜡烛的样品。这一支只完成了一半。然后把它们取下来，在一块细腻的石板上好好地滚一滚，用形状合适的管子把锥形的头塑出来，再把底部切掉、修整好。这一切做得如此精巧，他们用这种方法做出的蜡烛，可以恰好每磅四支，或六支，或随便多少支。

不过，我们不能在单纯的制造上再多花时间了，而要把问题再深入一点。我还没有给你们讲到蜡烛中的奢侈品（因为蜡烛里也有奢侈这回事）。看这些蜡烛染得多漂亮：你们看这里有苯胺紫、品红，以及最近才问世的各种化学染料的颜色，都用到了蜡烛上。你们还看到，蜡烛也采用了各种不同的形状。这里有一根带凹槽的柱子，形状十分优美；我这里还有几支皮尔索尔先生送来的蜡烛，上面饰有图案，所以它们燃烧时，可以说上面是一轮发光的太阳，下面是一束花。然而，凡是精美好看的，并不都是有用的。这些带凹槽的蜡烛虽然漂亮，却是坏蜡烛；它们之所以坏，就坏在外形上。尽管如此，我还是把四面八方好心的朋友送来的这些样品给你们看，让你们看看在这个或那个方向上已经做到了什么，还能做到什么；不过，正如我说过的，一讲究这些精巧，我们就不得不在用处上牺牲一点。

现在来说蜡烛的光。我们点上一两支，让它们干起它们的本行来。你们注意，蜡烛和油灯是很不相同的东西。用油灯，你要取一点油，把容器灌满，放进一点苔藓或者一些人工加工过的棉花，然后点燃灯芯的顶端。火焰顺着棉芯往下烧到油那里，就熄灭了，但在上面的部分它会继续燃烧。我毫不怀疑你们会问：油自己是不会燃烧的，它怎么会升到棉芯顶上、在那里燃烧呢？我们很快就来考察这个问题；不过，蜡烛的燃烧还有一件比这奇妙得多的事。这里你们有的是一种固体物质，没有容器盛着它；这种固体物质怎么能升到火焰所在的地方呢？它不是液体，怎么能到那里去？或者，当它变成液体之后，它又怎么能聚在一起不散开呢？这就是蜡烛的一件奇妙之处。

我们这里风很大，在有些演示中风会帮我们的忙，在另一些演示中却会捣乱；所以，为了稍稍有点规律，也为了把事情简化，我要造出一个安静的火焰——因为当路上横着一些与主题无关的困难时，谁还能好好研究那个主题呢？这里有一个巧妙的发明，是某个街头小贩或者市场上摆摊的人想出来的，他们星期六晚上卖青菜、土豆或者鱼的时候，用它来给蜡烛挡风。我常常赞赏这个东西。他们在蜡烛周围套上一个灯罩，用一种围廊似的托架撑着，托架箍住蜡烛，可以根据需要上下滑动。用这样的灯罩，照同样的方式使用，你就有了一个稳定的火焰，可以看着它，仔细地考察它——我希望你们回到家里也这样做。

你们看，首先，这里形成了一个美丽的杯。空气来到蜡烛旁，被蜡烛的热所产生的气流的力量带着向上走，它这样冷却了蜡、牛脂或别的燃料的四周，使边缘比里面凉得多；里面的部分被沿着烛芯尽量往下延伸、直到熄灭为止的火焰熔化了，外面的部分却不熔化。如果我造出一股朝某一个方向吹的气流，我的杯就会歪向一边，液体就会因此流溢出来——因为维系着诸天世界的同一种重力，也让这液体保持水平；如果杯不水平，液体当然就会流走，淌成烛泪。所以你们看，这个杯是由从四面八方吹拂着它、使蜡烛外围保持凉爽的那股美妙而有规律的上升气流造成的。凡是不具有形成这种杯的性质的燃料，都做不成蜡烛，只有像爱尔兰沼泽木那样的燃料除外，那种材料本身就像海绵，自己含着自己的燃料。现在你们明白了，如果你们去点我给你们看过的那些漂亮蜡烛，结果为什么会那么糟：它们形状不规则、凹凸不平，因此不可能有那种形状完好的杯沿，而那正是一支蜡烛的大美所在。我希望你们现在明白：一个过程的完善——也就是它的有用——才是它更好的美。对我们最有益的，不是最好看的东西，而是最好用的东西。这支好看的蜡烛，烧起来却很差。由于气流不规则，由此形成的杯也不好，它的四周会流下烛泪。当一小股烛泪顺着蜡烛的侧面流下来，使那里比别处厚的时候，你们可以看到上升气流作用的一些很好的例子（我希望你们留意这些例子）。随着蜡烛继续燃烧，那一小股烛泪留在原处，在蜡烛旁边形成一根竖着的小柱子；因为它比其余的蜡或燃料升得越高，周围的空气流通就越好，它被冷却得越厉害，在离热源稍远的地方也就越能抵抗热的作用。在蜡烛这件事上，正像在许多别的事情上一样，最大的错误和毛病，常常带给我们一些如果它们没有发生、我们就得不到的教益。我们来到这里，是要做哲学家；我希望你们永远记住：每当有一个结果发生，特别是一个新的结果，你们就应当问：“原因是什么？它为什么会发生？”久而久之，你们就会找到其中的道理。

其次，这些蜡烛还有一点可以回答一个问题——那就是，这种液体是以什么方式从杯里出来、沿着烛芯上升、到达燃烧之处的。你们知道，在用蜂蜡、硬脂或鲸蜡做的蜡烛里，这些燃着的烛芯上的火焰并不往下烧到蜡或别的物质那里，把它全部熔掉，而是守在自己该在的地方。它们和下面的液体隔开了，也不侵犯两边的杯。一支蜡烛使它的一部分为另一部分效力、直到它作用的最后一刻，这种调节得恰到好处的状态，是我所能想象的最美的例子。像这样一种可燃的东西，逐渐地烧下去，从不被火焰侵扰，是一幅非常美的景象；特别是当你们知道了火焰是何等猛烈的东西——它一旦抓住了蜡，有多大的力量把蜡本身毁掉，而它只要靠得太近，又有多大的力量扰乱蜡的本来形状。

可是火焰是怎样抓住燃料的呢？这里有一个很美的要点——*毛细引力*。“毛细引力！”你们会说，“就是毛发的吸引。”好吧，别管这个名字：它是很久以前起的，那时我们对真正起作用的力还没有很好的理解。正是靠所谓的毛细引力，燃料被输送到燃烧进行的地方，并沉积在那里，不是随随便便地，而是非常美妙地沉积在周围所发生的作用的正中心。现在我要给你们举一两个毛细引力的例子。正是这种作用或吸引力，使两种彼此不相溶解的东西仍然粘在一起。你们洗手的时候，把手彻底打湿；再用一点肥皂，使附着得更好，你们会发现手一直是湿的。这就是靠我要讲的这种吸引力。而且，如果你们的手不脏（手在日常生活里几乎总是脏的），你们把手指伸进一点温水里，水就会沿着手指往上爬一小段，虽然你们未必会停下来仔细察看。我这里有一种相当多孔的物质——一根盐柱——我要往底下的盘子里倒的，看上去是水，其实是不能再溶解更多盐的饱和盐溶液；所以你们将要看到的作用，不是由于它溶解了什么东西。我们可以把盘子看作蜡烛，把盐看作烛芯，把这种溶液看作熔化的牛脂。（我把液体染了色，好让你们更清楚地看到这种作用。）你们看，我现在把液体倒进去，它就往上升，沿着盐柱渐渐地越爬越高；只要盐柱不倒，它会一直爬到顶上。

如果这蓝色的溶液是可燃的，而我们在盐柱顶上放一根烛芯，它进入烛芯时就会燃烧。看着这种作用发生，观察它的某些情况是多么奇特，是一件极有意思的事。你们洗了手，拿毛巾擦掉水；正是靠那种使毛巾被水打湿的润湿作用，或者说那种吸引力，烛芯才被牛脂浸湿。我知道有些粗心的孩子（其实，我也知道细心的人身上发生过这种事），洗了手，用毛巾擦干，随手把毛巾搭在脸盆边上，不一会儿，毛巾就把盆里的水全吸出来，引到了地板上，因为它碰巧以那样的方式搭在盆边，正好起了虹吸管的作用。为了让你们更清楚地看到物质之间是怎样相互作用的，我这里有一个用金属丝网做成、装满了水的容器，你们可以在一方面把它的作用比作棉芯，在另一方面比作一块白棉布。实际上，烛芯有时就是用一种金属丝网做的。你们会看到，这个容器是多孔的；因为如果我在顶上倒一点水，水就会从底下流出来。如果我问你们，这个容器处于什么状态，里面有什么，为什么在那里，你们会困惑好一阵子吧？这个容器装满了水，可你们看，水从上面进去，又从下面流出来，好像它是空的一样。为了向你们证明这一点，我只要把它倒空就行了。道理是这样的：金属丝一旦被打湿，就一直是湿的；网眼非常小，液体从一边被如此强烈地吸引到另一边，以致尽管容器是多孔的，水仍然留在里面。同样，熔化的牛脂的微粒沿着棉芯上升，到达顶部；其他微粒凭着它们彼此之间的吸引力跟上来，它们一到火焰那里，就逐渐被烧掉了。

这是同一原理的另一个应用。你们看这一小段藤条。我见过街上那些急于显得像大人的男孩子，拿一段藤条点着了抽，模仿抽雪茄。他们之所以能这样做，是因为藤条顺着一个方向是通透的，又有毛细作用。如果我把这段藤条放在一个盛着一些莰烯油（它的一般性质与石蜡很相似）的盘子上，这种液体就会完全像那蓝色液体沿盐柱上升一样，沿着藤条上升。藤条侧面没有孔，液体不能往那个方向走，只能沿着它的长度方向通过。液体已经到了藤条顶端：现在我可以把它点着，让它当蜡烛用。液体是靠这段藤条的毛细引力升上去的，就像它沿着蜡烛里的棉芯上升一样。

蜡烛之所以不会沿着烛芯一直烧下去，唯一的原因是熔化的牛脂把火焰熄灭了。你们知道，如果把蜡烛倒过来，让燃料流到烛芯上，蜡烛就会熄灭。原因是火焰没来得及把燃料加热到能够燃烧的程度；而在上面，燃料是一小点一小点地被送进烛芯的，热对它充分发挥了作用。

关于蜡烛，还有一个条件你们必须了解，不然就不能完全理解它的道理，那就是燃料的蒸气状态。为了让你们明白这一点，让我给你们看一个非常好看、却又非常平常的实验。如果你们巧妙地把一支蜡烛吹灭，就会看到蒸气从它那里升起。我知道，你们常常闻到吹灭的蜡烛的蒸气——那气味很难闻；但如果你们巧妙地把它吹灭，就能相当清楚地看到这种固体物质所变成的蒸气。我要把其中一支蜡烛这样吹灭：不让我呼气的持续作用扰动它周围的空气；现在，如果我把一根点着的细烛放在离烛芯两三英寸的地方，你们就会看到一条火线穿过空气，一直烧到那支蜡烛上。我必须眼明手快，因为如果让蒸气有时间冷却，它就会凝结成液体或固体，或者那股可燃物质的气流就会被扰乱。

现在来说火焰的形状或形态。了解蜡烛的物质最后在烛芯顶端所呈现的状态，对我们非常重要——在那里，你们看到的美丽与光明，是只有燃烧或火焰才能产生的。

你们见过金银闪闪发光的美，见过红宝石和钻石那样的珠宝更高的光泽；但这些都比不上火焰的光辉与美丽。什么钻石能像火焰那样发光？它在夜里的光泽，正是靠火焰照在它上面。火焰在黑暗中发光，而钻石所有的光，在火焰照到它之前什么也不是，火焰一照到，它才又璀璨起来。唯有蜡烛是自己发光，为自己发光，或者说为那些安排好了这些材料的人发光。现在，我们来稍稍看看你们在玻璃罩下看到的火焰的形状。它稳定而均匀；它的一般形状就如图中所示，随着大气的扰动而变化，也随着蜡烛的大小而变化。它是一个明亮的长圆形——顶部比底部亮——烛芯在中间；除了中间的烛芯，靠近底部还有一些较暗的部分，那里的燃烧不像上面的部分那样完全。

我这里有一幅图，是胡克许多年前做研究时画的。画的是一盏油灯的火焰，但也适用于蜡烛的火焰。蜡烛的杯就是容器或灯，熔化的鲸蜡就是油，烛芯则是两者共有的。他在上面画了这一小团火焰，然后画出了一个真实的情况——有一定量的物质在火焰周围上升，这你们是看不见的，如果你们以前没来过这里，或者不熟悉这个题目，就不会知道它。他在这里画出了周围空气中对火焰非常重要、并且总是与火焰同在的那些部分。这里形成了一股气流，它把火焰拉长——因为你们看到的火焰，实际上是被气流拉长的，被向上拉到很高的地方——正如胡克在图中用延长的气流向你们表明的那样。你们可以这样来看：拿一支点着的蜡烛，放在阳光里，使它的影子投在一张纸上。那个亮得足以使其他物体产生影子的东西，竟然也能把它自己的影子投在一张白纸或白卡片上，使你们真的看到火焰周围有某种东西在流动，它不是火焰的一部分，却在上升，把火焰往上拉——这是多么了不起啊。现在，我要用伏打电池接上电灯，来模仿阳光。你们现在看到了我们的太阳和它强大的光；把一支蜡烛放在它和幕布之间，我们就得到了火焰的影子。

你们看到了蜡烛和烛芯的影子；然后是一个稍暗的部分，正如图中所示，再然后是一个更分明的部分。然而，奇怪的是，我们在影子里看到的火焰最暗的部分，实际上却是最亮的部分；在这里你们看到，热空气的上升气流在向上流动，正如胡克所画的那样，它把火焰拉长，给火焰供应空气，并冷却盛着熔化燃料的杯的四周。

这里我可以再给你们作一点演示，来表明火焰是怎样随着气流向上或向下的。我这里有一个火焰——不是蜡烛的火焰——不过到现在，你们无疑已经能够举一反三，把一件事和另一件事加以比较了。我要做的，是把那股把火焰往上带的上升气流，变成一股下降气流。用你们看到的我面前这个小装置，我很容易做到这一点。我说过，这个火焰不是蜡烛的火焰，而是由酒精产生的，这样它就不会冒太多的烟。我还要用另一种物质给火焰着色，好让你们追踪它的走向；因为单用酒精，你们几乎看不清楚，没法追踪它的方向。把这酒精点着，我们就有了一个火焰；你们看，把它举在空气中时，它自然是往上走的。

现在你们很容易明白，为什么在通常情况下火焰向上走——那是由于造成燃烧的那股空气的抽吸。但现在，把火焰往下吹，你们看，我就能让它向下走进这个小烟囱——气流的方向改变了。在这一系列讲座结束之前，我们会给你们看一盏灯，它的火焰向上而烟向下，或者火焰向下而烟向上。所以你们看，我们有能力用这种方法使火焰朝不同的方向变化。

现在还有另外几点我必须给你们讲讲。你们在这里看到的许多火焰，会因为从不同方向吹来的气流而大大改变形状；但只要我们愿意，我们可以使火焰看上去像固定不动的东西，可以给它们照相——的确，如果我们想弄清楚关于它们的一切，就必须给它们照相——使它们对我们来说固定下来。不过，这还不是我想说的唯一的事。如果我取一个足够大的火焰，它就不会保持那种均一的、一致的形状，而是带着一种十分奇妙的生命力迸发出来。我要用另一种燃料，但它确实可以公平地代表蜡烛的蜡或牛脂。我这里有一大团棉花，可以当烛芯用。现在，我已经把它浸在酒精里，并把它点着了，它和一支普通的蜡烛有什么不同呢？嗯，它在一个方面大不相同：它有一种活泼和力量，一种美和生命，与一支蜡烛所呈现的光完全不同。你们看那些美丽的火舌往上蹿。整团火焰从下往上的一般排布是一样的；但除此之外，还有这种显著的、迸裂成一条条火舌的情形，这在蜡烛上是看不到的。那么，这是为什么呢？我必须向你们解释，因为当你们完全理解了这一点，就能更好地跟上我以后要讲的内容。我想，在座的有些人自己就做过我要给你们看的这个实验。我猜在座有人玩过“抢火葡萄干”的游戏，对吗？就火焰的历史的某一部分而言，我不知道还有什么比“抢火葡萄干”的游戏更能美妙地说明火焰的道理了。首先，这里是盘子；让我告诉你们，要正经地玩这个游戏，盘子应当先烫得热热的；葡萄干和白兰地也应当是温热的，可惜这些我都没有。把酒倒进盘子，你们就有了杯和燃料；那些葡萄干不就像烛芯一样起作用吗？现在我把葡萄干扔进盘子，点燃酒，你们就看到了我说的那些美丽的火舌。空气从盘子边缘爬进来，形成了这些火舌。为什么？因为由于气流的力量和火焰作用的不规则，空气不能以一股均匀的气流流进来。空气流进来得如此不规则，本来会是单一的一个形象，就被打碎成种种形态，每一条小火舌都有它自己独立的存在。的确，我可以说，这里有许许多多独立的蜡烛。你们不要因为一下子同时看到这些火舌，就以为火焰就是这种特定的形状。那种形状的火焰，在任何一个时刻都不是那样的。一团火焰，就像你们刚才看到的从棉球上升起的那团，从来就不是它在你们看来的那种形状。它是由许多不同的形状组成的，这些形状一个接一个地出现得如此之快，以致眼睛只能把它们一下子全都收进来。从前我曾特意分析过一个具有这种一般特征的火焰，这幅图向你们表明了它是由哪些不同的部分组成的。它们并不是同时出现的：只是因为我们看到这些形状如此迅速地相继出现，它们在我们看来才好像同时存在。

真糟糕，我们还没能走得比我的抢火葡萄干游戏更远；但无论如何，我们都不能让你们超过时间。这对我将来是个教训：要让你们更严格地抓住事物的道理，而不要在这些演示上占用你们这么多时间。


最后一讲的结尾

这样你们就看到，呼吸与燃烧之间的类比变得更加美妙、更加动人了。的确，在这些讲座的最后（因为我们总要在某个时候结束），我所能对你们说的，只是表达一个愿望：愿你们在你们这一代人中，配得上与一支蜡烛相比；愿你们像它一样，成为照亮周围人的光；愿你们在一切行动中，以对同胞尽责时光明磊落、卓有成效的作为，不辜负这支细烛的美。