The origin and development of the atomic theory

SOURCES OF OUR INFORMATION

While the Atomic Theory is usually identified with the name of Democritus, its real founder was Leucippus, as is attested by both Aristotle (384-322 B. C.) and his successor, Theophrastus. Diogenes Laertius, who flourished about 230 of our era, refers to Leucippus (De Vitis, ix, 46) as the author of “The Great Diakosmos” (or “The Great Order of the Universe”), in which were set forth the principles upon which he based his atomic theory. A treatise “On the Mind” is also mentioned, which appears to have contained in outline the psychology of the materialistic Atomists.

Of the works of Leucippus there remains but one extant fragment, in which Leucippus lays down in clear terms this universal rule: “Nothing happens without a cause, but everything with a cause and by necessity” (Aetius, Doxographers 321 B. 10).

Following in the footsteps of his master, Democritus also wrote a book “On the Order of the Universe,” adhering, it would seem, very closely to the views of Leucippus. The works of his master the great Milesian, were incorporated eventually in the collected works of Democritus.

No writer, subsequent to Theophrastus (born at Lesbos about 390 B. C., died in 286 B. C.), pupil of and successor to Aristotle as head of the famous Lyceum at Athens, attempted to distinguish the teaching of Leucippus from that of his more brilliant disciple. Zeller remarks that “the work and even the name of Leucippus seems to have been pretty early forgotten by most writers in comparison with the riper and more exhaustive achievements of his disciple. The persistence with which he is ignored by Epicurus, the reviver of the Atomistic philosophy, and by most of the Epicureans, may have contributed to this.[6]

Of the once numerous writings of Democritus himself, only fragments remain, but these are highly important. The chief collector of the extant fragments was Mullach,[7] who places Democritus first on the list of Greek philosophers for genius and knowledge, and thinks it probable that the great Aristotle himself may owe much of his reputation for learning to diligent perusal of the words of the sage of Abdera. Says he: “(Democritus), although in other things dissimilar, in his equal study of all the arts was most like the famous Aristotle. And I scarcely know whether the Stagirite did not owe to his reading of the works of Democritus his erudition, which surpassed that of all other philosophers.”

Aristotle and some later historians make frequent references to his teachings, and according to Zeller, “with respect.” Gompertz says that Aristotle confers “a crown of eulogy” upon Democritus “at the expense of Plato.”

Professor Lange remarks, however, that “he cites him, for the most part, only when he attacks him, and this he by no means always does with a fitting objectivity and fairness. How often he has borrowed from him without naming him we do not know. Plato speaks of him nowhere, though it is a matter of dispute whether, in some places, he has not controverted his opinion without mention of his name” (“History of Materialism,” page 18).

It seems to be quite possible that Plato knew little or nothing of the writing of Democritus. At any rate, they were not well known in Athens before Aristotle’s discussion of his theories. An extant Democritean fragment states that “I went to Athens and no one knew me.” Professor Burnet says: “It is not clear that Plato knew anything about Democritus, for the few passages in the Timæus and elsewhere where he seems to be reproducing him are easily explained by the Pythagorean influences that affected them both. Aristotle, on the other hand, knows Democritus well; for he too was an Ionian from the north.

“It is certain, nevertheless, that the Democritean corpus (which included the works of Leucippus and others as well as those of Democritus) continued to exist; for the school maintained itself at Abdera and Teos down to Hellenistic times. It was therefore possible for Thrasyllos in the reign of Tiberius to produce an edition of the works of Democritus arranged in tetralogies just like his edition of Plato’s dialogues. Even that did not suffice to preserve them.”[8]

Besides being the favorite pupil of Leucippus, Democritus (according to Glaubus of Rhegion, a contemporary) had also Pythagoreans for teachers, including the astronomer, geometrician and physician, Philolaus, who was exiled from Italy in the first half of the fifth century B. C. because of his membership in the Pythagorean Order. Burnet thinks that this accounts not only for Democritus’ geometrical knowledge but also “for other features of his system.”

THE PHYSICS OF DEMOCRITUS

We know that both Leucippus and Democritus regarded the atoms composing the various substances of the world as being homogeneous—i.e., all alike from a chemical stand-point, but differing from one another in point of size and in rich variety of form. Unlike the minute particles (homœomeries) of Anaxagoras, which were assumed to be infinitely divisible as well as qualitatively different for each substance, the atoms of Leucippus and Democritus were considered indivisible; hence the name atoma (atoms) (particles which cannot be cut, or further divided).

But while the atoms are described as “indivisible,” because there is no vacuum in them, this does not mean that they were regarded by Leucippus and Democritus as mere mathematical points, like the atoms of Boscovich[9] or the “point charges” (electrons) of some modern physicists. They were bodies of a definite magnitude, some larger, others smaller, but never of visible size (Sextus, Mathematica, vii, 139), much less, as asserted by Stobæus (Eclagarum physicarum et ethicarum, i, 348) “as large as a world.” According to Simplicius (Physica, 18 a), Democritus taught that the atoms were physically indivisible, but he did not claim that they were mathematically indivisible.

The variety of substances and organisms seen on every hand is due entirely, according to Democritus—and also to Leucippus, whose views are expressed by Democritus—to the infinite variety of the atoms in form, size and arrangement in space with reference to one another—an anticipation of modern stereochemistry (the arrangement of the atoms of a molecule in space) and the work of van’t Hoff (1852-1911).[10] In all other respects the atoms are alike, and act on one another only by pressure or collision.

THE ATOMIC THEORY OF KNOWLEDGE

Man’s sense impressions—color, sound, bitterness, sweetness, etc.—are merely the effect of the impact of atoms upon a particular grouping or arrangement of physically varied but essentially (chemically) homogeneous atoms, constituting our sense organs. Hence these sense qualities have no existence in themselves—are mere deceptive “appearances.” “Only in opinion consists sweetness, bitterness, cold, color; in truth there is nothing but the atoms and empty space,” says Democritus.

The great Protagoras (born about 500 B. C.), also of Abdera, a contemporary of Leucippus and Democritus, had taught that all sensations are equally true for the sentient subject—i.e., if a substance tastes sweet to a given person, it is sweet. For Democritus sweetness and bitterness did not reside as such in the substance tasted, but were merely subjective effects produced on the palate of the consumer. Taste is partly dependent upon the shape of the atoms composing the food (they held) and partly upon the particular taste-sense of the individual. Thus to the normal (or average) person honey has a sweet taste, whereas the same honey to a jaundiced person has a bitter taste.

Parmenides had already declared that taste, colors, sound and the like were only names, standing for no objective qualities. Democritus agreed that sensations represent nothing external to ourselves, though they are caused by something outside us. For example, what we call pungency, tartness, bitterness, saltiness, etc., were impressions produced on the palate by atoms of a certain shape—sharp, rough, pointed or hooked particles of matter producing an effect of pungency or acidity. Atoms with smooth surfaces form substances which ordinarily impress the senses agreeably. From this we learn the effect upon our palates of certain substances, but these sensations tell us nothing of the true nature of the substances tasted.

“By the senses,” says Democritus, “we in truth know nothing sure, but only something that changes according to the disposition of the body and of the things that enter into it or resist it” (Fragment 9). True reality lies beyond sense impressions; “truth is in the depths” (Fragment 11). Our ideas represent our impressions, and are not direct reproductions of the external objects themselves, “the inner essence of which is concealed from us.”

This ancient theory of the differences of taste depending on differences in the shapes—or roughness or smoothness—of the particles composing substances prevailed even well into the eighteenth century of our own era; dictionaries of the period still defining acidity, for example, as due to sharp, pointed particles. Today we still admit that atoms are qualitatively homogeneous—but by “atoms” we now mean electrons, the constituent electrical charges which make up the “atoms” of the chemist. Differences in the number of electrons in atoms confer upon them qualitative (chemical) differences, though all atoms of any one element are chemically alike—are homogeneous. Differences in the number of spatial arrangement of these atoms (in groups or “molecules”) constitute both physical and chemical differences in substances, i.e., in compounds. Quite different substances are produced by combinations of precisely the same kinds of atoms, but in different proportions.

Take from a molecule of certain substances one single atom, and they may be changed from a compound necessary to life and growth into a deadly poison. Phosphorus is an element, and thus contains but one kind of atoms; but some (common) phosphorus is yellow and some (amorphous) is red, varying with the spatial distribution of the atoms in the molecules composing the phosphorus.

But the properties (or quality) of a compound are not merely the sum of the qualities of the different kinds of atoms composing its molecules (a molecule being the smallest possible quantity of a given substance or compound). Water, for example, is not merely the addition of the qualities of one atom of oxygen to those of two atoms of hydrogen (H₂O). It is something quite different from either of these two elements. And just so the color of blue sulphate of copper is not a mere mixture of the colors of sulphuric acid and copper. Again, the experiments of Dr. P. W. Bridgman[11] showed that while the application of ordinary pressures to ice causes it to melt, the application of high pressures to water causes it to freeze, and that “there are at least five different kinds of ice, only one of which we are ordinarily familiar with” (Page 192). Paraffin, under pressures as high as 20,000 atmospheres, “becomes more rigid than soft steel” (Page 188). Water, heretofore regarded as absolutely incompressible, was found to decrease in volume about twenty per cent with a pressure under 12,000 atmospheres.

Professor W. T. Marvin could well say, in considering the shortcomings of ancient atomic theories, that “even with our wealth of physical information we cannot yet explain by a rigorous atomistic mechanics water transforming into ice or a stick of wood burning, not to mention the phenomena of living organisms.”

Modern science recognizes that not only different results may be obtained under different conditions, but that absolutely new qualities emerge at critical moments, both in the domain of chemistry and in the phenomena of biology. We talk now of emergent evolution. “We live in a world in which there seems to be an orderly sequence of events.... But the orderly sequence, historically viewed, appears to present, from time to time, something genuinely new.... If there be only regrouping of pre-existing events and nothing more—then there is no emergent evolution.”[12]

In the gradual transition from non-living to living matter, an entirely new and peculiar type of energy—“biotic energy” emerges, which is not explicable merely on the grounds of increasing complexity of atomic structure. “We call things living because of the energy changes they exhibit, and not because they are complex chemically or physically.” A dead animal is just as complex as a living organism. What is missing is “biotic energy”—the form of energy which gives rise to the distinctive energy-transformations “which we aggregate together under the term life.” The recognition of this fact, however, does not commit us to the outworn doctrine of “vitalism” or to the Aristotelian “entelechy.”[13]

Leucippus and Democritus, of course, were not troubled with the problems raised by such phenomena as we have just been considering, since they knew nothing about them. For the founders of Atomism, a multiplicity of substances, living matter, and consciousness could readily be accounted for by the varied combination of variously formed atoms, physically considered. What would be their astonishment to learn that tens of thousands of different substances are actually composed of only four kinds of atoms—viz., hydrogen, oxygen, nitrogen and carbon! Yet for them one element, qualitatively considered, was sufficient to produce all that is—including the “soul”—provided this primal matter existed in an infinite number of shapes and sizes of atomic dimensions.

DEMOCRITEAN COLOR THEORY

“We have no exact information,” says Professor Gompertz, “as to which bodies in the theory of Democritus were simple and which were complex,” but he adduces evidences to show that “the infinite multiplicity which Democritus recognized in the sizes and shapes of atoms did not arise from his incompetence to perceive or to conjecture a complex in an apparently simple body.”

He remarks that the Democritean theory of color started from the assumption of four primary colors—white, black, red and green. “These, with the exception of green, which had taken the place of yellow, were likewise the primary colors in the scheme of Empedocles.” But all other colors “were designated as mixed, and we see that all the numerous bodies which were not equipped with one of the four primary colors must have been of a composite nature. That is to say, they must have included other than merely homogenously elementary particles.... The statements about the atomic forms underlying the several tastes give rise at first impression (to the idea that) each of the countless ‘juices’ or materials of taste is composed of homogeneous atoms possessing the size and shape required for the purpose.

“But this, we plainly perceive, was not the opinion of Democritus. His own view of the mixed colors cries against it. The homogeneity of the atoms was admissible in the case of white salt, but it was not admissible in that of yellow-gold honey or of brownish-yellow human bile. It is true that he must have referred the sweetness of the one and the bitterness of the other to the presence of the atomic forms by which these impressions were produced. But yellow and brown were mixed colors in his theory, and he must accordingly have inferred that honey and bile alike contained atoms of other forms as well.”

Professor Gompertz therefore concludes that “the true meaning of those statements should therefore be expressed as follows: ‘In all substance of mixed colors at least the kind of atoms which lends them their specific taste is merely the predominant and preponderant kind, and without wasting more words on this subject, Theophrastus, who is our best authority for Democritus’ theory of sensation, relates that this doctrine was expressly taught by him’.”[14]