Part 3

These varied causes of destruction may be seen constantly at work by any one who looks for them. They act from the moment of birth, being more especially destructive to the young; and, as only one in ten or fifty or a thousand (according to the rate of increase of the particular species) can possibly come to the full breeding age, we feel compelled to ask ourselves: What determines the nine or the forty-nine or the nine hundred and ninety-nine, as the case may be, which die, and the one which survives? Darwin calls this process of extermination one of “natural selection”—that is, by this process nature weeds out the weak, the unhealthy, the unadapted, the imperfect in any way. Of course, what may be called chance or accident produces many deaths of individuals otherwise well fitted to live, but if we think of the process going on day by day and year by year till only one in a hundred of those born in a given area are left alive, it is impossible to suppose that the _one_ which has passed through all the dangers and risks which have been fatal to, say, his ninety-nine relations was not, in all the faculties and qualities essential to the continuance of the race, decidedly better organized than the bulk of those which succumbed. Herbert Spencer calls the process the “survival of the fittest,” and though the term may not be strictly accurate in the case of any one species in any one year, yet when we consider that the struggle is going on _every_ year, during the whole duration of each species, we cannot doubt that, on the whole, and in the long run, those which survive are among the fittest. The struggle is so severe, so incessant, that the smallest defect in any sense organ, any physical weakness, any imperfection in constitution, will almost certainly, at one time or another, be fatal.

This continual weeding out of the less fit, in every generation, and with exceptional severity in recurring adverse seasons, will produce two distinct effects, which require to be clearly distinguished. The first is the preservation of each species in the highest state of adaptation to the conditions of its existence; and, therefore, so long as these conditions remained unchanged, the effect of natural selection is to keep each well-adapted species also unchanged. The second effect is produced whenever the conditions vary, when, taking advantage of the variations continually occurring in all well-adapted and therefore populous species, the same process will slowly but surely bring about complete adaptation to the new conditions. And here another fact—the normal variability of all populous or dominant species, which is seldom realized except by those who have largely and minutely compared the individuals of many species in a state of nature—comes into play. There are some writers who admit all the preceding facts and reasoning, so far as the action of natural selection in weeding out the unfit and thus keeping every species in the highest state of efficiency is concerned, but who deny that it can modify them in such a way as to adapt them to new conditions, because they allege that “the right variations will not always occur at the right time.” This seems a strong and real objection to many of their readers, but to those who have studied the variability of species in nature, it is a mere verbal difficulty dependent on ignorance of the actual facts. A brief statement of the facts must therefore be given.

Of late years, and chiefly since Darwin’s works were written, the variability of animals and plants in a state of nature has been carefully studied, by actual comparison and measurement of scores, hundreds, and even thousands of individuals of many common, that is, abundant and widely distributed species; and it is found that in almost every case they vary greatly, and, what is still more important, that every organ and every appendage varies independently and to a large amount. Some of the best known of these facts of variation are adduced in my _Darwinism_, and are illustrated by numerous diagrams, and much more extensive series have since been examined, always with the same general result. By large variability is meant a variation of from ten to twenty-five per cent. on each side of the mean size, this amount of variation occurring in at least five or ten per cent. of the whole number of individuals, and in every organ or part as yet examined, external or internal.

Now, as the weeding-out process is so severe, only from one in ten to one in a hundred of those born surviving to produce young, the above proportion of variations affords ample scope for the selection of any variation needed in order to modify the species so as to bring it into harmony with new or changing conditions. And this will be the more easy and certain if we consider how slowly land-surfaces and climates undergo permanent changes; and these are certainly the kind of changes that initiate and compel alterations, first, perhaps, in the distribution, and afterwards in the structure and habits of species. It follows, therefore, as an absolutely necessary conclusion from the facts, if natural selection can and does keep each continually varying species in close adaptation to an unchanging environment, that it preserves the fixity of its mean or average condition, and almost every objector admits this. Then, given a slowly changing environment, the same power must inevitably bring about whatever corresponding change is needed for the well-being and permanent survival of the various species which are subjected to those changed conditions.

I shall not add here a further consideration of the objections and difficulties alleged by critics of the theory. All of these have, I believe, been fully answered either by Darwin or myself, many of the most recent having been discussed in review articles. Suffice it to say here that this theory of natural selection—meaning the elimination of the least fit, and therefore the ultimate “survival of the fittest”—has furnished a rational and precise explanation of the means of adaptation of all existing organisms to their conditions, and therefore of their transformation from the series of distinct but allied species which occupied the earth at some preceding epoch. In this sense it has actually demonstrated the “origin of species,” and, by carrying back this process step by step into earlier and earlier geological times, we are able mentally to follow out the evolution of all forms of life from one or a few primordial forms. Natural selection has thus supplied that motive power of change and adaptation that was wanting in all earlier attempts at explanation, and this has led to its very general acceptance both by naturalists and by the great majority of thinkers and men of science.

The brief sketch now given of the progress of human thought on the questions of the fact and the mode of the evolution of the material universe indicates how great has been the progress during the nineteenth as compared with all preceding centuries.

Although the philosophical writers of classical times obtained a few glimpses of the action of law in nature regulating its successive changes, nothing satisfactory could be effected till the actual facts had been better ascertained by the whole body of workers who, during the last five centuries, have penetrated ever more and more deeply into nature’s mysteries and laws. By their labors we became possessed of such a body of carefully observed facts that, towards the end of the eighteenth century, such thinkers as Laplace and Hutton were enabled to give us the first rudiments of theories of evolution as applied to the solar system and the earth’s crust, both of which have been greatly developed and rendered more secure during the century just passed away.

In like manner Buffon and Goethe may be said to have started the idea of organic evolution, more systematically treated a little later by Lamarck, but still without any discovery of laws adequate to produce the results we see everywhere in nature. The subject then languished, till, after twenty years of observation and research, Charles Darwin produced a work which at once satisfied many thinkers that the long-desired clew had been discovered. Its acceptance by almost the whole scientific world soon followed: it threw new light on almost every branch of research, and it will probably take its place, in the opinion of future generations, as the crowning achievement of the nineteenth century.

ALFRED RUSSEL WALLACE.

CHEMISTRY

The progress of the science of chemistry forms one phase of the progress of human thought. While at first mankind was contented to observe certain phenomena, and to utilize them for industrial purposes, if they were found suitable, “philosophers,” as the thinking portion of our race loved to call themselves, have always attempted to assign some explanation for observed facts, and to group them into similars and dissimilars. It was for long imagined, following the doctrines of the Greeks and of their predecessors, that all matter consisted of four elements or principles, names which survive to this day in popular language. These were “fire,” “air,” “water,” and “earth.” It was not until the seventeenth century that Boyle in his _Sceptical Chymist_ (1661) laid the foundations of the modern science, by pointing out that it was impossible to explain the existence of the fairly numerous chemical substances known in his day, or the changes which they can be made to undergo, by means of the ancient Greek hypotheses regarding the constitution of matter. He laid down the definition of the modern meaning of the word “element”; he declined to accept the current view that the properties of matter could be modified by its assimilating the qualities of fire, air, earth, or water, and he defined an element as the _constituent_ of a compound body. The first problem, then, to be solved, was to determine which of the numerous forms of matter were to be regarded as elementary, and which are compound, or composed of two or more elements in a state of combination; and to produce such compounds by causing the appropriate elements to unite with each other.

One of the first objects to excite curiosity and interest was the air which surrounds us, and in which we live and move and have our being. It was, however, endowed with a semi-spiritual and scarcely corporeal nature in the ideas of our ancestors, for it does not affect the senses of sight, smell, or taste, and though it can be felt, yet it eludes our grasp. The word “gas,” moreover, was not invented until Van Helmont devised it to designate various kinds of “airs” which he had observed. The important part which gases play in the constitution of many chemical compounds was accordingly overlooked; and, indeed, it appeared to be almost as striking a feat of necromancy to produce a quantity of a gas of great volume from a small pinch of solid powder as for a “Jinn” of enormous stature but of delicate texture to issue from a brass pot, as related in the _Arabian Nights Entertainments_. Gradually, however, it came to be recognized, not merely that gases have corporeal existence, but that they even possess weight. This, though foreshadowed by Torricelli, Jean Rey, and others, was first clearly proved by Black, professor of chemistry in Edinburgh, in 1752, through his masterly researches, as carbonic acid.

The ignorance of the material nature of gases and of their weight lies at the bottom of the “Phlogistic Theory,” a theory devised by Stahl about the year 1690, to account for the phenomena of combustion and respiration and the recovery or “reduction” of metals from their “earths” by heating with charcoal or allied bodies. According to this inverted theory, a substance capable of burning was imagined to contain more or less phlogiston, a principle which it parted with on burning, leaving an earth deprived of phlogiston, or “dephlogisticated,” behind if a metal. This earth, when heated with substances rich in phlogiston, such as coal, wood, flour, and similar bodies, recovered the phlogiston, which it had lost on burning, and, with the added phlogiston, its metallic character. Other substances, such as phosphorus and sulphur, gave solids or acid liquids, to which phlogiston was not so easy to add; but even they could be rephlogisticated. On this hypothesis, it was the earths, and such acid liquids as sulphuric or phosphoric acids, which were the elements; the metals and sulphur and phosphorus were their compounds with phlogiston.

The discovery of oxygen by Priestley and by Scheele in 1774, and the explanation of its functions by Lavoisier during the following ten years, gave their true meaning to these phenomena. It was then recognized that combustion was union with oxygen; that an “earth” or “calx” was to be regarded as the compound of a metal with oxygen; that when a metal becomes tarnished, and converted into such an earthy powder, it is being oxidized; that this oxide, on ignition with charcoal or carbon, or with compounds such as coal, flour, or wood, of which carbon is a constituent, gives up its oxygen to the carbon, forming an oxide of carbon, carbonic oxide on the one hand, or carbonic “acid” on the other, while the metal is reproduced in its “reguline” or metallic condition, and that the true elements are metals, carbon, sulphur, phosphorus, and similar bodies, and not the products of their oxidation.

The discovery that air is in the main a mixture of nitrogen, an inert gas, and oxygen, an active one, together with a small proportion of carbonic “acid” (or, as it is now termed, anhydride)—a discovery perfected by Rutherford, Black, and Cavendish—and that water is a compound with oxygen of hydrogen, previously known as inflammable air, by Cavendish and by Watt, finally overthrew the theory of phlogiston; but at the beginning of this century it still lingered on, and was defended by Priestley until his death in 1804. Such, in brief, was the condition of chemical thought in the year 1800. Scheele had died in 1786, at the early age of forty-four; Lavoisier was one of the victims of the French Revolution, having been guillotined in 1794; Cavendish had ceased to work at chemical problems, and was devoting his extraordinary abilities to physical problems of the highest importance, while living the life of an eccentric recluse, and Priestley, driven by religious persecution from England to the more tolerant shores of America, was enjoying a peaceful old age, enlivened by occasional incursions into the region of sectarian controversy.

The first striking discovery of our century was that of the compound nature of the alkalies and of the alkaline earths. This discovery was made by Humphry Davy. Born in Cornwall in 1778, he began the study of chemistry, self-taught, in 1796; and in 1799 he became director of the “Pneumatic Institution,” an undertaking founded by Dr. Beddoes, at Bristol, for the purpose of experiments on the curative effects of gases in general. Here he at once made his mark by the discovery of the remarkable properties of “laughing gas,” or nitrous oxide. At the same time he constructed a galvanic battery, and began to perform experiments with it in attempting to decompose chemical compounds by its means. In 1801 Davy was appointed professor of chemistry at the Royal Institution, a society or club which had been founded a few years previously by Benjamin Thompson, Count Rumford, for the purpose of instructing and amusing its members with recent discoveries in chemistry and natural philosophy. In 1807 Davy applied his galvanic battery to the decomposition of damp caustic potash and soda, using platinum poles. He was rewarded by seeing globules of metal, resembling mercury in appearance, at the negative pole; and he subsequently proved that these globules, when burned, reproduced the alkali from which they had been derived. They also combined with “oxymuriatic acid,” as chlorine (discovered by Scheele) was then termed, forming ordinary salt, if sodium be employed, and the analogous salt, “muriate of potash,” if the allied metal, potassium, were subjected to combustion. By using mercury as the negative pole, and passing a current through a strong solution of the chloride of calcium, strontium, or barium, Davy succeeded in procuring mixtures with mercury or “amalgams” of their metals, to which he gave the names calcium, strontium, and barium. Distillation removed most of the mercury, and the metal was left behind in a state of comparative purity. The alkali metals, potassium and sodium, were found to attack glass, liberating “the basis of the silex,” to which the name silicon has since been given.

Thus nearly the last of the “earths” had been decomposed. It was proved that not merely were the “calces” of iron, copper, lead, and other well-known metals compounds of the respective metals with oxygen, but Davy showed that lime, and its allies, strontia and baryta, and even silica or flint, were to be regarded as oxides of elements of metallic appearance. To complete our review of this part of the subject, suffice it to say that aluminum, a metal now produced on an industrial scale, was prepared for the first time in 1827 by Wöhler, professor of chemistry at Göttingen, by the action of potassium on its chloride, and alumina, the earthy basis of clay, was shown to be the oxide of the metal aluminum. Indeed, the preparation of this metal in quantity is now carried out at Schoffhausen-on-the-Rhine and at the Falls of Foyers, in Scotland, by electrolysis of the oxide dissolved in melted cryolite, a mineral consisting of the fluorides of sodium and aluminum, by a method differing only in scale from that by means of which Davy isolated sodium and potassium in 1806.

To Davy, too, belongs the merit of having dethroned oxygen from its central position among the elements. Lavoisier gave to this important gas the name “oxygen,” because he imagined it to be the constituent of all acids. He renamed the common compounds of oxygen in such a manner that the term oxygen was not even represented in the name—only inferred. Thus a “nitrate” is a compound of an oxide of nitrogen and an oxide of a metal; a “sulphate,” of the oxide of a metal with one of the oxides of sulphur, and so on. Davy, by discovering the elementary nature of chlorine, showed, first, that it is not an oxide of hydrochloric acid (or muriatic acid as it was then called); and, second, that the latter acid is the compound of the element chlorine with hydrogen. This he did by passing chlorine over white-hot carbon—a substance eminently suited to deprive oxy-compounds of their oxygen—and proving that no oxide of carbon is thereby produced; by acting on certain chlorides, such as those of tin or phosphorus with ammonia, and showing that no oxide of tin or phosphorus is formed; and, lastly, by decomposing “muriatic acid gas” (gaseous hydrogen chloride) with sodium, and showing that the only product besides common salt is hydrogen. Instead, therefore, of the former theory that a chloride was a compound of the unknown basis of oxymuriatic acid with oxygen and the oxide of a metal, he introduced the simpler and correct view that a chloride is merely a compound of the element chlorine with a metal. In 1813 he established the similar nature of fluorine, pointing out that on the analogy of the chlorides it was a fair deduction that the fluorides are compounds of an undiscovered element, fluorine, with metals; and that hydrofluoric acid is the true analogue of hydrochloric acid. The truth of this forecast has been established of recent years by Henri Moissan, who isolated gaseous fluorine by subjecting a mixture of hydrofluoric acid and hydrogen potassium fluoride contained in a platinum U tube to the action of a powerful electric current. He has recently found that the tube may be equally well constructed of copper; and this may soon lead to the industrial application of the process. The difficulty of isolating fluorine is due to its extraordinary chemical energy; for there are few substances, elementary or compound, which resist the action of this pale yellow, suffocating gas. In 1811 iodine, separated by Courtois from the ashes of sea-plants, was shown by Davy to be an element analogous to chlorine. Gay-Lussac subsequently investigated it and prepared many of its compounds; and in 1826 the last of these elements, bromine, was discovered in the mother-liquor of sea-salt by Balard. The elements of this group have been termed “halogens,” or “salt producers.”

While Davy was pouring his researches into the astonished ears of the scientific and dilettante world, John Dalton, a Manchester school-master, conceived a theory that has proved of the utmost service to the science of chemistry, and which bids fair to outlast our day. It had been noticed by Wenzel, by Richter, by Wollaston, and by Cavendish, towards the end of the last century, that the same compounds contain the same constituents in the same proportions, or, as the phrase runs, “possess constant composition.” Wollaston, indeed, had gone one step farther, and had shown that when the vegetable acid, oxalic acid, is combined with potash, it forms two compounds, in one of which the acid is contained in twice as great an amount relatively to the potash as in the other. The names _monoxalate_ and _binoxalate_ of potash were applied to these compounds, to indicate the respective proportions of the ingredients. Dalton conceived the happy idea that by applying the ancient Greek conception of atoms to such facts the relative weights of the atoms could be determined. Illustrating his views with the two compounds of carbon with hydrogen, marsh gas and olefiant gas, and with the two acids of carbon, carbonic oxide, carbonic “acid,” he regarded the former as a compound of one atom of carbon and one of hydrogen, and the second as a compound of one atom of carbon and two of hydrogen, and similarly for the two oxides of carbon. Knowing the relative weights in which these elements enter into combination, we can deduce the relative weights of the atoms. Placing the relative weight of an atom of hydrogen equal to unity, we have:

Marsh Olefiant | Carbonic Carbonic Gas Gas | Oxide Acid Carbon 6 6 | Carbon 5 6 Hydrogen 1 2 | Oxygen 8 16

Thus the first compound, marsh gas, was regarded by Dalton as composed of an atom of carbon in union with an atom of hydrogen; or, to reproduce his symbols, as ⊜◉; while the second, olefiant gas, on this hypothesis, was a compound of two atoms of hydrogen with one of carbon, or ◉◍◉. Similarly the symbols ◍○, and ○◍○ were given to the two compounds of carbon with oxygen. So water was assigned the symbol ◉○, for Dalton imagined it to be a compound of one atom of hydrogen with one of oxygen. Compounds containing only two atoms were termed by him “binary”; those containing three, “ternary”; four, “quaternary,” and so on. The weight of an atom of oxygen was eight times that of an atom of hydrogen; while that of an atom of carbon was six times as great as the unit. By assigning symbols to the elements, consisting of the initial letters of their names, or of the first two letters, formulas were developed, indicating the composition of the compound, the atomic weights of the elements being assured. Thus, NaO signified a compound of an atom of sodium (natrium), weighing twenty-three times as much as a similar atom of hydrogen, with an atom of oxygen, possessing eight times the weight of an atom of hydrogen. Therefore, thirty-one pounds of soda should consist of twenty-three pounds of sodium in combination with eight pounds of oxygen, for, according to Dalton, each smallest particle of soda contains an atom of each element, and the proportion is not changed, however many particles be considered.