The origin and development of the atomic theory

THE SIGNIFICANCE OF THE ATOMIC THEORY

It is safe to say that there is no more romantic story in the history of science than that of the origin and development of the atomic theory of matter. Dr. Robert A. Millikan has said that the physical principles laid down by Leucippus in the fifth century before our era might, with a few modifications and omissions, “almost pass muster today” (“The Electron,” Page 7). The importance to modern students of sound knowledge of the teachings of the ancient Atomists was emphasized by Sir William Osler (1829-1919), who even went so far as to say that “the student of physics may know Crookes’ tubes and their relation to Roentgen, but he cannot have a true conception of the atomic theory without a knowledge of Democritus; and the exponent of Madame Curie and of Sir J. J. Thomson will find his happiest illustrations from the writings of Lucretius”[1]—the Roman exponent of Epicurus (342-270 B. C.), who revived the atomic theory of Leucippus and Democritus, despite the adverse criticisms hurled at this doctrine by the great Aristotle.

Le Sage observed that “if Epicurus had had but a part of the geometrical knowledge of his contemporary Euclid, and conceptions of cosmogony the same as many then living, he might have discovered the laws of universal gravity, and not only the laws, but, what was the despair of Newton, its mechanical cause” (“Lucrèce Newtonien,” Berlin Academy, 1782).

Writing of the value to science and modern thought of the atomic theory of the early Greek philosophers, Professor Walter T. Marvin, of Rutgers College, points out that a theory can be significant in at least three ways, namely:—“(1) by destroying or inhibiting other beliefs; (2) by arousing interest in new problems and by suggesting new methods of investigation; (3) by what it itself enables us to explain correctly. This theory was most significant in destroying old beliefs or, to adopt a much used expression, in ‘enlightening’ the cultured Greeks. A thoughtful Greek could hardly believe that the universe is a cloud of atoms moving about in accordance with necessary mechanical laws, and at the same time continue to believe the primitive traditions and superstitions of his people. The worship of the gods and the old magical rites and ceremonies must needs seem to him utterly ineffective and useless, valuable customs no doubt for their purely psychological influence upon the ignorant and unruly masses but of course absurdities for the cultured and disciplined man. Hence no wonder that the spread of this and the preceding cosmological theories would result, in a society such as that of the Greek world in the sixth and fifth centuries B. C., in a radical enlightenment. No wonder that their spread was opposed by men of conservative tendencies. In this first respect early Greek science and in particular the atomic theory were of great historical significance.”[2]

THE ATOMIC THEORY OF THE PYTHAGOREANS

In the ancient Sanskrit literature of India (written prior to 500 B. C.), an atomic theory of matter is formulated by Kanada (literally “atom eater”—a term of derision), founder of the Nyaga system of philosophy, and said to have been a pupil of Buddha. He states that the atoms are eternal and that the ultimate atom is simple.

Kapila, the leading exponent of the Sankhya philosophy, speaks of “five subtle” kinds of particles (atoms), and a substance akin to our luminiferous ether—the five particles being, no doubt, the “five elements” of the Laws of Menu; viz., earth, water, wind (air), fire and ether—this last the parent, so to speak, of all the other elements, through a process of successive transformations.

In the “Angutarra Nikaja,” consciousness (mind) is mentioned as a sixth element, also atomic in structure.

In his “History of Hindu Chemistry,” Sir P. C. Ray expresses the opinion that the atomic theory of the ancient Greeks was derived directly from the more ancient Hindu doctrine—a view upheld by the great German Sanskrit scholar, Dr. Max Müller, as also by some Greek scholars.

The atomic theory, the earliest known to have been worked out in detail, is that of the Greek philosopher Leucippus, of Miletus, Ionia; though the mantle of honor has fallen mostly on the shoulders of his far better known pupil, Democritus of Abdera, Thrace.

But the Pythagoreans also were exponents of a form of atomic theory, and it seems probable that Pythagoras, a native of the island of Samos, was the first Greek to advance the doctrine of the discontinuity of matter. At least, none of his disciples ever claimed to have been the originator of this doctrine, and Pythagoras was born some time between 580 and 570 B. C., while the Atomic School of Leucippus was not founded until some time after 500 B. C. Unfortunately, Pythagoras did not commit his doctrines to writing, though a few of the so-called “Golden Sentences” may have been written by him. Most of them, however, are probably no older than the fourth century of our era. Moreover, these throw no light on the subject under discussion.

The first written exposition of the Pythagorean atomic theory was put forward by Philolaus, a native of Tarentum, South Italy. Only fragments of his work have survived, and of those ascribed to him some are undoubtedly spurious. But all of them are very old and contain valuable information concerning Pythagorean doctrines.

Porphyry (233-304? A. D.), a Syrian Neo-Platonist, residing for some years in Alexandria, wrote a “Life of Pythagoras,” and a few years later another “Life” of this philosopher appeared, this time from the pen—or stylus—of another Syrian and Neo-Platonist, Iamblichus. But these works contain much that is wholly mythical concerning Pythagoras.[3]

Our best sources of information are Plato (Timaeus), Aristotle (Metaphysica and Physica, De Anima and De Caelo), Diogenes Laertius (De Vitis) and Stobaeus (Eclogarum physicarum et ethicarum). From these authorities we learn that, according to the Pythagoreans, the cosmos was at a certain stage of its (cyclic) changes a compact, inert, spherical mass of lifeless matter, having no distinguishable parts. After a long period of quiescence the “void”—i. e., the limitless outer air—broke in upon the world, entering into “the heaven itself” as if it—the heaven—were breathing. The result of this cosmic inhalation was “a certain separation and definition of things that lie together” (Aristotle, Physica, iv, 6)—that is, a separation of the homogeneous mass into different “elements.” These fragments were eventually ground into an all but infinite number of infinitesimal particles, or “monads,” analogous to the “atoms” of Leucippus and Democritus.

Now, Philolaus was a famous geometrician as well as an eminent physician and astronomer. Hence he—and presumably Pythagoras before him—thought of these particles (or atoms) not in terms of various qualities, chemically considered,—as Anaxagoras (500-428 B. C.), who was not a Pythagorean, had done before Philolaus wrote—but in terms of form (shape) and number. Each of the various substances known to the ancient world as “elements”—generally recognized as compounds of the real elements since the eighteenth century only—was regarded as made up of particles of a certain geometrical configuration. Philolaus explained that the “element” earth was composed of cubical particles, fire of tetrahedra (pyramidal forms), and the “ether” was identified with the dodecahedron (particles having twelve plane faces, or twelve regular pentagons). In the Timaeus of Plato we find this conception further developed, bringing all the five regular solids into the theory. Thus, the octahedron was now assigned to air, and the icosahedron (a figure having twenty equilateral triangular faces) to water.

Very interesting in this connection is the fact that the positions of the electrons in atoms (the real elements) are being referred to today in terms similar to those employed by the Pythagoreans. Take, for example, the following passage from Science Progress (London), July, 1922 (No. 65), Pages 21-22:

But we know now that “fire” is not an “element” composed of tetrahedral atoms; but the combustible portion of coal and wood is the real element carbon—and the carbon molecule is of tetrahedral form. (See Bragg, Sir W. H. and W. L., “X-Rays and Crystal Spectra.”)

On the Pythagorean theory—as on that of Leucippus, and on the latest theories of today—matter is broken up into parts (atoms) that are in themselves unchangeable—apart from radioactivity—but produce by their changes of position in relation to one another all the substances of earth and of living organisms.

To illustrate this principle in terms of modern science: Add four electrons (two positive and two negative) to the hydrogen atom, and you have the element lithium; knock out of the lithium atom (composed of three positive and three negative electrons) one positive and one negative electron, and you have one atom of helium (composed of two positive and two negative electrons.) And electrons are all alike, except that some carry a charge of positive electrification and some a negative charge—each kind (species) of atom having an equal number of positive and negative charges, thus attaining stable equilibrium. (See Soddy, The Interpretation of Radium, 1922.)

Until quite recently it was believed that atoms could be disrupted only by temperatures higher than those obtainable in our physical laboratories, or by bombardment by electrons and helium atoms spontaneously expelled (always with enormous velocities) from radioactive substances. But this is now known to be an erroneous assumption. It was lately discovered by P. M. Basset, engineer of the Sperry Gyroscope Company, and Dr. Louis Bell, that when carbon is brought to a temperature of 5,000° C., in an arc-light used in connection with their amazingly powerful searchlight, alpha particles (helium atoms) are liberated. Such discoveries may some day lead to the transmutation of “the baser metals into gold,” thus fulfilling the dream of the alchemists of old.

Quite recently, Drs. Milliken and Bowen not only developed a method for “stripping” planetary (valence) electrons one by one from atoms, but these investigations also proved that Bohr’s (simple) theory of electron orbits—which includes the statement that the energy developed when an electron jumps from one orbit to another is exactly proportional to the frequency (or wave-length) emitted—is correct. Professor Sommerfeld’s theory explaining the cause of double lines in the spectrum of hydrogen and other elements was also verified experimentally. (See The Scientific Monthly, Pages 665-669, June, 1924).

An atom of mercury, for example, contains 80 positive charges (electrons) on its nucleus, and 80 negative outlying electrons. Were we able to expel two of its protons (positive electrons), it would instantly become the metal platinum. If a negative (“planetary”) electron were also taken from it, the mercury atom would then have lost two positive charges (electrons) and one negative; that is, one positive charge on the whole: and hence it would retain 79 positive charges on the nucleus and 79 outlying negative electrons—and thus become gold!

Thus, one element differs from another only in the number of electrons composing its atom. And this is only a more precise statement of the essential doctrine of the ancient Greek atomists.

Parmenides, the Eleatic philosopher, who was at the height of his fame about 475 B. C., declared that both motion and change of substance were illusory—that no substances ever transform from one to another. The Pythagoreans and the School of Leucippus admitted that there was, indeed, an element of elements that knew no change, no transformations; and they declared that this primal element was the stuff that all atoms are made of. Today we believe his primal element (atom) to be hydrogen—as was suggested by the English physician, William Prout, in 1815. In other words, we are being forced by the mathematical and experimental data to conclude that all of the 87 known species of atoms (or elements) are but compounds of the original (simplest) hydrogen atom, consisting of one positively charged nuclear electron and one outlying negative electron. However, there is ground for difference of opinion on this question, as shown by Sir Oliver Lodge in his recent article, “Within the Atom,” Scientific American, November, 1923.

“Thought,” comments Professor Alfred Weber (“History of Philosophy,” Pages 43-44), “discovers in the atomistic hypothesis the middle term that unites Parmenides, who denies the great empirical fact of generation and change, and Heraclitus, who sacrifices being and its permanence to becoming,—thereby combining the two rival systems into a higher synthesis,—and lays the foundation for every rational explanation of the process of becoming. Henceforth philosophy no longer regards matter as a continuous mass, the essential properties of which are incessantly transformed. It breaks them up into parts that are in themselves immutable, but which continually change their relative positions. As a consequence, there can be both perpetual change in the aspects of matter (bodies) and permanence in the essence and properties of matter. All change is reduced to change of place: mechanism.”

THE FIERY “MONADS” (ATOMS)

“Fire,” with the Pythagoreans, as with the followers of Heraclitus of Ephesus (535-475 B. C.), is the element par excellence; and, as previously stated, was regarded by them as made up of excessively minute particles of tetrahedral (pyramidal) form (Philolaus). This “subtile element” was looked upon as the symbol of the divine principle in nature. They taught that this “fire” is concentrated in a central sun, “the hearth of the universe,” “mother of the gods,” “citadel of Zeus,” etc., around which revolve the earth and the other heavenly bodies.[4] The soul of man is a portion of the world-soul, a spark of the celestial fire, and in this sense material.

Aristotle states (De Anima, i, 2) that some of the Pythagoreans held the solar corpuscles (atoms) to be souls, while others referred to that which set them in motion as the soul. Schlottman’s reading of this passage is: “The solar corpuscles are moved by a soul, and the soul is, generally speaking, the moving principle.”

Professor Burnet calls attention to the singular power exhibited by the Pythagoreans in adapting their theories to conditions; and among certain radical changes in their point of view, he thinks the most remarkable is the way the religious side of the doctrine was gradually dropped. “The effort was made to clear the name of Pythagoras himself from the imputation of mysticism. We have the echo of this in the remains of Aristoxenos and Dikairchos, but it must be older; for in their day scientific Pythagoreans had ceased to exist. The statement that Hippasos of Metapontium was guilty of publishing a mystic discourse ‘with the view of misrepresenting Pythagoras’ (Diogenes, viii, 7) must go back to this generation of the school; for at a later date no one would have any interest in making it.”[5]

According to Stobaeus (Eclogarum physicarum et ethicarum, i, 308), Ecphantus—an immediate successor of Pythagoras, according to Röth—was the first philosopher to explain the Pythagorean monads (atoms) as something corporeal. But this view is regarded by most authorities as being contrary to the doctrine of the Pythagoreans. While Ecphantus is included among the disciples of the School, his doctrine of material atoms as the original constituents of the Pythagorean “numbers,” as well as of matter, cannot, according to Zeller, have been derived from his reputed master. Unlike the followers of Leucippus, Ecphantus believed, with Anaxagoras (500-428 B. C.), that the movement of the atoms (or monads), as well as the formation of the universe, was produced by mind or soul. Atoms, according to Ecphantus, differ among themselves in size, form and force. It is interesting to note that this philosopher had not only accepted as true the affirmation of Pythagoras that the earth is a sphere, but he knew also that it rotated upon its axis (Schiaparelli, “I Precursori di Copernico nell’Antichita,” in Memorie del Reale Instituto Lombardi, xii).

Here, then, paradoxically enough, we find in the teachings of the idealistic Pythagoreans the roots of our modern theories of cosmogony and the atomic theory of matter. Their “particles” are qualitatively all alike, differing only in form. By changes in their number and position these qualitatively homogeneous atoms form all the various substances of earth, sea and sky.

THE “SEEDS” OF ANAXAGORAS (500-428 B. C.)

The “seeds” (or germs) of Anaxagoras must also, in a sense, be considered “atoms.” But, so far from being all alike fundamentally, for him each substance was supposed to be composed of its own peculiar particles, there being as many kinds of “seeds” as there are kinds of substances.

Whence came this more or less novel doctrine? Was it wholly original with the sage of Clazomeniæ? Leucippus, the founder of “the materialistic” atomic theory, was a contemporary of Anaxagoras, and both lived after the time of Pythagoras, and may have been indebted either to him or to suggestions from India for their fundamental physical conceptions, finding them, indeed, fully accordant with the primary postulates of the older Ionian physicists—Anaximines (524-508 B. C.), Anaximander (611-547 B. C.) and Thales (624?-548? B. C.). All of these believed that all elements are but compounds or transformations of one primitive element.

It is natural to inquire here how such “suggestions from India” could have reached Greece. Professor Gompertz, while he does not discuss the possible Indian origin of the atomic theory, would have an answer to this question. He admits that the Greeks “owe to the Orient the elements of material civilization” and much of their science, art and religion to older civilizations. How were these transferred to Greece? This question, he recalls, brings up a striking parallel from the literary history of mediæval Europe. “Practically the entire fairy-lore of the Occident is derived from India. No one,” he goes on to say, “disputes this assertion today”; yet, on the other hand, “no one as yet can give a completely clear account of the ways and means by which its journey was accomplished” (“Greek Thinkers,” Page 95).