If in building a house that is to stand when the rains fall and the winds blow, it is requisite6 to go down to the solid rock for a foundation, so much the more is it necessary in building up a theory to begin at the beginning and give it a solid groundwork. Nine-tenths of the fallacies current in the world arise from the haste with which people rush to conclusions on insufficient7 premises8. Take, for instance, any of the political questions of the day, such as the Irish question: how many of those who express confident opinions, and get angry and excited on one side or the other, could answer any of the preliminary questions which are the indispensable conditions of any rational judgment9? How many marks would they get for an examination paper which asked what was the population of Ireland; what proportion of that population was agricultural; what proportion of that agricultural population consisted of holders10 of small tenements11; what was the scale of rents compared with that for small holdings in other countries;[10] how much of that rent was levied12 on them for their own improvements; and other similar questions which lie at the root of the matter? In how many cases would it be found that the whole superstructure of their confident and passionate13 theories about the Irish difficulty was based on no more solid foundation than their like or dislike of a particular statesman or of a particular party?
I propose therefore to begin at the beginning, and, taking the simplest case, that of dead or inorganic14 matter, show how the material universe is built up by the operation of the all-pervading law of polarity. What does matter consist of? Of molecules, and molecules are made up of atoms, and these are held together or parted, and built up into the various forms of the material universe, primarily by polar forces.
Let me endeavour to make this intelligible15 to the intelligent but unscientific reader. Suppose the Pyramid of Cheops shown for the first time to a giant whose eye was on such a scale that he could just discern it as a separate object. He might make all sorts of ingenious conjectures17 as to its nature, but if microscopes had been invented in Giant-land and he looked through one, he would find that it was built up, layer by layer, on a regular plan and in determinate lines and angles, by molecules, or what seemed to him almost infinitely18 small masses, of squared stone. For pyramid write crystal, and we may see by the human sense, aided by human instruments and human reason, a similar structure built up in the same way by minute particles. Or again, divide and subdivide19 our iron filings until we reach the limit of possible mechanical division discernible by the microscope; each one remains20 essentially21 a[11] bar of iron, as capable of being magnetised, and showing the same qualities and behaviour under chemical tests as the original bar of iron from which the filings were taken. This carries us a long way down towards the infinitely small, for mechanical division and microscopic22 visibility can be carried down to magnitudes which are of the order of 1/100000th of an inch.
But this is only the first step; to understand our molecules we must ascertain4 whether they are infinitely divisible, and whether they are continuous, expanding by being spread out thinner and thinner like gold-beater’s skin: or are they separate bodies with intervals23 between them, like little planets forming one solar system and revolving24 in space by fixed25 laws. Ancient science guessed at the former solution and embodied26 it in the maxim27 ‘that nature abhors28 a vacuum’: modern science proves the latter.
In the first place bodies combine only in fixed proportions, which is a necessary consequence if they consist of definite indivisible particles, but inconceivable if the substance of each is indefinitely divisible. Thus water is formed in one way and one only: by uniting one volume or molecule1 of oxygen with two of hydrogen, and any excess of one or the other is left out and remains uncombined. But if the molecules could be divided into halves, quarters, and so on indefinitely, there can be no reason why their union should take place always in this one proportion and this only.
A still more conclusive29 proof is furnished by the behaviour of substances which exist in the form of gases. If a jar is filled with one gas, a second and third gas can be poured into it as readily as into a vacuum, the result being that the pressure on the sides[12] of the jar is exactly equal to the sum of the separate pressures of each separate gas. This evidently means that the first gas does not occupy the whole space, but that its particles are like a battalion30 of soldiers in loose skirmishing order, with such intervals between each unit that a second and third battalion can be marched in and placed on the same ground, without disturbing the formation, and with the result only of increasing the intensity31 of the fire.
Now gas is matter as much as solids or liquids, and in the familiar instance of water we see that it is merely a question of more or less heat whether the same matter exists as ice, water, or steam. The number and nature of the molecules is not changed, only in the one case they are close to one another and solidly linked together; in the other, further removed and free to move about one another, though still held together as a mass by their mutual32 attractions; and in the third, still further apart, so that their mutual attraction is lost and they dart33 about, each with its own proper motion, bombarding the surface which contains them, and by the resultant of their impacts producing pressure.
In this latter and simpler form of gas the following laws are found to prevail universally for all substances. Under like conditions volumes vary directly as the temperature and inversely34 as the pressure. That is to say, the pressure which contains them remaining the same, equal volumes of air, steam, or any other substance in the state of gas, expand into twice the volume if the temperature is doubled, three times if it is tripled, and so on; contracting in the same way if the temperature is lowered. If on the other hand the temperature remains constant, the volume is reduced to one[13] half or one third, if the pressure is doubled or tripled. From these laws the further grand generalisation has been arrived at, that all substances existing in the form of gas contain the same number of molecules in the same volume.
This, which is known as the Law of Avogadro, from the Italian chemist by whom it was first discovered, is the fundamental law of modern chemistry, and the key to all certain and scientific knowledge of the constitution of matter and of the domain35 of the infinitely small, just as much as the law of gravity is to action of matter in the mass, and the resulting conditions and motions of mechanics and astronomy.
This conclusion obviously follows from it, that difference of weight in different substances arises not from one having more molecules in the same volume than another, but from the molecules themselves being heavier. If we weigh a gallon or litre of hydrogen gas, which is the lightest known substance, and then weighing an equal volume of oxygen gas find that it is sixteen times heavier, we know for certain that the molecule or ultimate particle of oxygen is sixteen times heavier than that of hydrogen.
It is evident that in this way the molecules of all simple substances which can exist in the form of pure gas can be weighed, and their weight expressed in terms of the unit which is generally adopted, that of the molecule of the lightest known substance, hydrogen. But science, not content with this achievement, wants to know not the relative weight only, but the absolute dimensions, qualities, and motions of these little bodies; and whether, although they cannot be divided further by mechanical means, and while retaining the qualities[14] of the substances they build up, they are really ultimate and indivisible particles or themselves composites.
Chemistry and electricity give a ready answer to this latter question. Molecules are composites of still smaller bodies, and to get back to the ultimate particle we must go to atoms. All chemical changes resolve themselves into the breaking up of molecules and rearrangement of their constituent36 atoms. If the opposite poles of a voltaic battery are inserted in a vessel37 containing water, molecules of water are broken up, bubbles of gas rise at each pole, and if these are collected, the gas at the positive pole is found to be oxygen, and that at the negative pole hydrogen. Nothing has been added or taken away, for the weight of the two gases evolved exactly equals that of the water which has disappeared. But the molecules of the water have been broken up, and their constituents38 reappear in totally different forms, for nothing can well be more unlike water than each of the two gases of which it is composed. That it is composed of them can be verified by the reverse experiment of mixing the two gases together in the same proportion of two volumes of hydrogen to one of oxygen as was produced by the decomposition39 of water, passing an electric spark through the vessel containing the mixture, when with a loud explosion the gases reunite, and water is formed in precisely40 the same quantity as produced the volumes of gas by its decomposition. Can the ultimate particles of these gases be further subdivided41; can they, like those of water, be broken up and reappear in new forms? No; there is no known process by which an atom of oxygen can be made anything but oxygen, or an atom of hydrogen anything but hydrogen.
[15]
The only thing which is compound in the composition of oxygen is that its molecules consist of two atoms linked together. This appears from the fact that while the weight of oxygen, and therefore that of its molecules, is sixteen times greater than that of an equal volume of hydrogen, and therefore of hydrogen molecules, it combines with it in the proportion not of sixteen, but of eight to one. If, therefore, the molecule were identical with the atom of oxygen, we must admit that the atom could be halved42, which is contrary to its definition as the ultimate indivisible particle of the substance oxygen. But if the oxygen molecule consists of two linked atoms, O—O, and the hydrogen molecule equally of two, H—H, as can be proved by other considerations, everything is explained by assuming that the molecule of water consists of two atoms of hydrogen linked to one of oxygen, or H?O, and that when this molecule is broken up by electricity, its constituents resolve themselves into atoms, which recombine so as to form twice as many molecules of hydrogen, H—H, as of oxygen, O,—i.e. into two volumes of hydrogen gas to one of oxygen.
Taking the single hydrogen atom as the unit of weight as being the lightest known ponderable body, and calling this weight a microcrith, or standard of the smallest of this order of excessively small weights, this is equivalent to saying that the weight of an oxygen atom is equal to 16 microcriths, and as water is composed of one such atom plus two of hydrogen, the weight of its molecule ought to be 16 + 2 = 18, which is in fact the exact ratio in which the weight of a volume of steam, or water in the form of gas, is heavier than an equal volume of hydrogen.
[16]
This key unlocks the whole secret of the chemical changes and combinations by which matter assumes all the various forms known to us in the universe.
Thus oxygen enters into a great variety of combinations forming different substances, but always in the proportion which is either 16, or some multiple of 16, such as 32, 48, 64. That is, either 1, 2, 3, or 4 atoms of oxygen unite with other atoms to form the molecules from which these other substances are made.
One atom of oxygen weighing 16 microcriths combines, as we have seen, with two atoms of hydrogen weighing 2, to form a molecule of water weighing 18 mc. In like manner one atom of oxygen, 16 mc., combines with one of carbon, which weighs 12 mc., to form a molecule of carbonic oxide43 weighing 28 mc.; and two of oxygen, 32 mc., with one of carbon, 12 mc., to form a molecule of carbonic dioxide weighing 44 mc.
The same applies to all elementary substances. Thus hydrogen, two atoms of which combine with one of oxygen to form water, combines one atom to one with chlorine to form the molecule of hydrochloric acid, which weighs 36·5 mc., being the united weights of one atom of chlorine, 35·5 mc., and one of hydrogen, 1 mc. These, with hundreds of similar instances, are the results not of theories as to molecules and atoms, but of actual facts, ascertained by innumerable experiments made independently by careful observers over long periods of years, many of them dating back to the labours of the alchemists of the middle ages in pursuit of gold. The atomic theory is the child and not the parent of the facts, and is indeed nothing but the summary of the vast variety of experiments which led up to it, as Newton’s law of gravity is of the facts[17] known to us with regard to the attractions and motions of matter in the mass. But as Newton’s law enables us to predict new facts, to calculate eclipses and the return of comets beforehand, and to compile nautical44 almanacs; so the new chemistry, based on the atomic theory, affords the same conclusive proof of its truth by enabling us in many cases to predict phenomena45 which are subsequently verified by experiment, and to infer beforehand what combinations are possible, and what will be their nature.
The actual existence, therefore, of molecules and atoms is as well-ascertained a fact, as that of cwts. and lbs., or of planets and stars, of solar systems and nebul?.
The researches of chemists have succeeded in discovering about 70 substances, of which the same may be said as of the oxygen and hydrogen into which water is decomposed46, viz. that they cannot be decomposed by any known process, and must therefore be considered as ultimate and elementary. Their atoms differ widely in size and weight: that of mercury, for instance, being 200 times heavier than that of hydrogen, and the weights varying from 1 mc. for the hydrogen atom, up to 240 for that of uranium. When we call them elementary substances, we merely mean that we know no means of decomposing47 them. It is possible that all of them may be compounds which we cannot take to pieces of some substratum of uniform matter, and it is remarkable48 that the weight of nearly all of these elementary atoms is some simple multiple of that of hydrogen, pointing to their being all combinations of one common substratum of matter; but this is merely conjecture16, and in the present state of our knowledge we must assume these 66 or 71 ultimate particles[18] or atoms to be the indivisible units out of which all the complicated puzzle of the material universe is put together. They are not all equally important to us. Of the 71 elementary substances enumerated49 in chemical treatises50, 5 are doubtful, and 30 to 35 of the remainder are either known only to chemists in minute quantities, or exist in nature in small quantities, having no very material bearing upon man’s relation to matter. The most important are oxygen, hydrogen, nitrogen, and carbon. Oxygen diluted51 by nitrogen gives us the air we breathe, combined with hydrogen the water we drink, and with metals and other primitive52 bases the solid earth on which we tread. Carbon again is the great basis of organised matter and life, to which it leads up by a variety of complex combinations with oxygen, hydrogen, and nitrogen.
The qualities and relations of elementary atoms afford a subject of great interest, but of such vast extent that those who wish to understand it must be referred to professed53 works on modern chemistry. For the present purpose it is sufficient to say that the following conclusions are firmly established.
All the various forms of matter are composed of combinations of primitive atoms which form molecules, the molecules being neither more nor less than very small pieces of ordinary matter.
The qualities of this matter, or, what is the same thing, of its molecules, depend partly on the qualities of the atoms, which are something quite distinct from those of the molecules, and partly on their mode of aggregation54 into molecules, affecting the form, size, stability, and other attributes of the molecule.
All matter, down to the smallest atom, has definite[19] weight and is indestructible. No man by taking thought can add the millionth of a milligramme to the weight of any substance, or make it either more or less than the sum of the weights of its component55 factors, any more than he can add a cubit to his stature56. When Shelley sang of the cloud,
I change, but I cannot die,
he enunciated57 a scientific axiom of the first importance. Creation, in the sense of making something out of nothing, is a thing absolutely unknown and unknowable to us. If we say we make a ship or a steam-engine, we simply mean that we transform existing matter and existing energies into new combinations, which give results convenient for our purpose. So if we talk of making a world, our idea really is that if our powers and knowledge were indefinitely increased we might be able, given the atoms and energies with their laws of existence, to put them together so as to produce the desired results. But how the atoms and their inherent laws got there is a question as to which knowledge, or even conceivability, is impossible, for it altogether transcends58 human experience.
Before finally taking leave of atoms it may be well to state shortly that science, not content with having proved their existence and weighed them in terms of the lightest element, the hydrogen atom, has attempted, not without success, to solve the more difficult problem of their real dimensions, intervals, and velocities. This problem has been attacked by Clausius, Sir W. Thomson, Clerk Maxwell, and others, from various sides: from a comparison with the wave-lengths of light; with the tenuity of the thinnest films of soap-bubbles just before[20] they burst, and when they are presumably reduced to a single layer of molecules; and from the kinetic59 theory of gases, involving the dimensions, paths, and velocities of elastic60 bodies, constantly colliding, and by their impacts producing the resulting pressure on the confining surface. All these methods involve such refined mathematical calculations that it is impossible to explain them popularly, but they all lead to nearly identical results, which involve figures so marvellous as to be almost incomprehensible. For instance, a cubic centimetre of air is calculated to contain 21 trillions of molecules—i.e. 21 times the cube of a million, or 21 followed by 18 ciphers61; the average distance between each molecule equals 95 millionths of a millimetre, which is about 25 times smaller than the smallest magnitude visible under a microscope; the average velocity62 of each molecule is 447 metres per second; and the average number of impacts received by each molecule in a second is 4,700 millions.
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1
molecule
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| n.分子，克分子 | |
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molecules
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| 分子( molecule的名词复数 ) | |
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velocities
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| n.速度( velocity的名词复数 )；高速，快速 | |
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ascertain
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| vt.发现，确定，查明，弄清 | |
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ascertained
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| v.弄清，确定，查明( ascertain的过去式和过去分词 ) | |
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6
requisite
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| adj.需要的，必不可少的；n.必需品 | |
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7
insufficient
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| adj.(for，of)不足的，不够的 | |
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8
premises
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| n.建筑物，房屋 | |
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judgment
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| n.审判；判断力，识别力，看法，意见 | |
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10
holders
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| 支持物( holder的名词复数 )； 持有者； （支票等）持有人； 支托（或握持）…之物 | |
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tenements
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| n.房屋，住户，租房子( tenement的名词复数 ) | |
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12
levied
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| 征（兵）( levy的过去式和过去分词 )； 索取； 发动（战争）； 征税 | |
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13
passionate
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| adj.热情的，热烈的，激昂的，易动情的，易怒的，性情暴躁的 | |
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inorganic
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| adj.无生物的；无机的 | |
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intelligible
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| adj.可理解的，明白易懂的，清楚的 | |
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16
conjecture
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| n./v.推测，猜测 | |
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conjectures
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| 推测，猜想( conjecture的名词复数 ) | |
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18
infinitely
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| adv.无限地，无穷地 | |
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subdivide
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| vt.细分（细区分，再划分，重分，叠分，分小类） | |
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20
remains
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| n.剩余物，残留物；遗体，遗迹 | |
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essentially
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| adv.本质上，实质上，基本上 | |
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microscopic
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| adj.微小的，细微的，极小的，显微的 | |
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intervals
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| n.[军事]间隔( interval的名词复数 )；间隔时间；[数学]区间；（戏剧、电影或音乐会的）幕间休息 | |
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revolving
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| adj.旋转的，轮转式的；循环的v.（使）旋转( revolve的现在分词 )；细想 | |
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fixed
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| adj.固定的，不变的，准备好的；(计算机)固定的 | |
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embodied
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| v.表现( embody的过去式和过去分词 )；象征；包括；包含 | |
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maxim
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| n.格言，箴言 | |
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abhors
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| v.憎恶( abhor的第三人称单数 )；（厌恶地）回避；拒绝；淘汰 | |
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conclusive
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| adj.最后的，结论的；确凿的，消除怀疑的 | |
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battalion
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| n.营；部队；大队(的人) | |
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intensity
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| n.强烈，剧烈；强度；烈度 | |
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mutual
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| adj.相互的，彼此的；共同的，共有的 | |
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dart
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| v.猛冲，投掷；n.飞镖，猛冲 | |
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inversely
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| adj.相反的 | |
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domain
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| n.(活动等)领域，范围；领地，势力范围 | |
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constituent
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| n.选民；成分，组分；adj.组成的，构成的 | |
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vessel
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| n.船舶；容器，器皿；管，导管，血管 | |
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constituents
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| n.选民( constituent的名词复数 )；成分；构成部分；要素 | |
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decomposition
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| n. 分解, 腐烂, 崩溃 | |
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40
precisely
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| adv.恰好，正好，精确地，细致地 | |
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41
subdivided
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| 再分，细分( subdivide的过去式和过去分词 ) | |
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42
halved
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| v.把…分成两半( halve的过去式和过去分词 )；把…减半；对分；平摊 | |
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43
oxide
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| n.氧化物 | |
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nautical
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| adj.海上的，航海的，船员的 | |
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45
phenomena
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| n.现象 | |
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46
decomposed
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| 已分解的，已腐烂的 | |
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47
decomposing
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| 腐烂( decompose的现在分词 )； （使）分解； 分解（某物质、光线等） | |
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48
remarkable
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| adj.显著的，异常的，非凡的，值得注意的 | |
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49
enumerated
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| v.列举，枚举，数( enumerate的过去式和过去分词 ) | |
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50
treatises
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| n.专题著作，专题论文，专著( treatise的名词复数 ) | |
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51
diluted
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| 无力的，冲淡的 | |
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52
primitive
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| adj.原始的；简单的；n.原(始)人，原始事物 | |
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53
professed
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| 公开声称的，伪称的，已立誓信教的 | |
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54
aggregation
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| n.聚合，组合；凝聚 | |
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55
component
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| n.组成部分，成分，元件；adj.组成的，合成的 | |
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56
stature
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| n.（高度）水平，（高度）境界，身高，身材 | |
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57
enunciated
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| v.（清晰地）发音( enunciate的过去式和过去分词 )；确切地说明 | |
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58
transcends
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| 超出或超越（经验、信念、描写能力等）的范围( transcend的第三人称单数 )； 优于或胜过… | |
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59
kinetic
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| adj.运动的；动力学的 | |
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elastic
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| n.橡皮圈，松紧带；adj.有弹性的；灵活的 | |
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61
ciphers
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| n.密码( cipher的名词复数 )；零；不重要的人；无价值的东西 | |
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velocity
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| n.速度，速率 | |
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