The 19th-Century Atomic War

Author’s note: This lecture was delivered at the Objectivist Summer Conference of 2003. It has been edited for publication here.

Most people think physical science is immune to the outcome of debates among philosophers. Even people who see how philosophy can influence subjects such as literature, economics, and history have difficulty seeing how it can influence physics or chemistry. They assume that the universally accepted methods of experiment and mathematics constrain the physical sciences to follow the facts, regardless of what philosophers might say.

When I tell people that my field is philosophy of physics, they often react as if I told them that I study the mating habits of rocks or the migratory flights of pigs. Even in today’s world, they insist, there are a few things one can rely upon—namely, rocks don’t mate, pigs don’t fly, and a “hard” science like physics doesn’t have anything to do with philosophy. This last, however, is dead wrong; the science of physics is utterly dependent upon philosophy, and cannot exist or advance a single step without it.

As Ayn Rand argued, philosophy is inescapable. It deals with the fundamental ideas that necessarily guide the thinking and the actions of all men.1 Let us begin by reviewing her argument as it applies to the science of physics.

Metaphysics is the branch of philosophy that deals with the nature of existence as a whole, or, in Aristotle’s words, with “being qua being.” It identifies, in terms of the broadest essentials, what kind of world we live in. Metaphysics answers such questions as: Is the universe a realm of real entities with specific natures, or is it a realm of pseudo-entities that can exist without specific properties? Is it a causal realm ruled by natural law, or a realm of inexplicable miracles ruled by a supernatural power, or an unintelligible chaos ruled by chance? Is it a realm of objects that are what they are independent of anyone’s consciousness, or is it a realm of “appearances” created in the mind of the subject? Are the facts of reality absolute, or do they change with our perspective? Is the universe eternal, or did it spring into existence as a product of supernatural ideas?

The basic view of the world held by physicists is contained in their answers to such questions—and different answers will necessarily lead to very different theories of physics.

Epistemology is the branch of philosophy that studies the nature of knowledge and man’s means of acquiring it. It answers such questions as: Do our abstract ideas derive from our perception of particulars in reality, or are such ideas (as Einstein claimed) “free inventions of the human mind”? Do abstractions refer to real things, or arbitrarily selected groups of “mental images”? What is logic? Is it an objective method enabling us to identify facts without contradiction, or a linguistic game with rules set by social convention? What is truth? Is it the correspondence between an individual’s ideas and the facts, or a consensus of belief among the members of some group? Can we know reality by means of reason, and if so, how? Are there means of acquiring knowledge other than reasoning from the data provided by our senses, such as innate ideas, intuitions, revelations, feelings, and so on? Can reason yield certainty, or are we doomed to perpetual doubt?

A physicist’s view of his basic goal, and his means of achieving it, depend on his answers to these questions.

It is true that most physicists (like other people) do not give such questions a great deal of thought. But this does not mean that they are able to proceed in their life and work without any answers; rather, it means that they passively absorb their philosophic views from others and proceed accordingly. Although only a small number of men originate philosophic ideas, the ideas are disseminated throughout the culture in countless ways by schools, churches, media, and the arts. They are implied more often than explicitly stated, but years of such implications leave an indelible impression. The power of philosophy is sometimes hidden, but always real.

The above is a brief statement of a very abstract argument for the dependence of physics on philosophy. However, such wide abstractions represent knowledge only when they are integrations of countless concretes; empty abstractions are useless. There is a universal law that applies here: The less data you put into an argument, the less understanding you get out of it.

In order to gain a real understanding of this topic, one must study the history of the two subjects and grasp the influence of philosophy on physics in a whole array of concrete cases spanning centuries. When one sees repeatedly how the philosophic ideas of each era affect the theories proposed by physicists in that era, then the abstract argument is no longer empty.

My goal here is simply to illustrate this thesis by examining one particular case. The case I have chosen is from the 19th century, when scientists finally proved the atomic nature of matter. This is one of the greatest discoveries in the history of science and it provides an eloquent demonstration of the role of philosophy. Let us begin by setting the historical context for this magnificent achievement.

The existence of atoms was originally proposed in ancient Greece for the wrong reasons. The Greek atomists did not start with observations; instead, they started with a strange view originated by the philosopher Parmenides. They accepted from Parmenides the conclusion that “being” (by which he meant existence) is incompatible with change in general and with motion in particular. So, in order to explain change and motion, the atomists proposed the existence of non-being or the void. Thus they arrived at the idea that the universe consists of tiny immutable pieces of existence swimming around in a vast sea of non-existence. The little pieces of existence were called atoms.

Notice that the theory of the Greek atomists was deduced from a philosophic mistake, rather than induced from scientific evidence. The Greeks had no scientific evidence to support the idea that matter is made of atoms, nor would anyone have such evidence for a long time to come. Historically, the idea of atoms was born prematurely—and, to make matters worse, it was born alongside an evil twin: the idea of the existence of nothingness. It was not a promising start.

If we follow the idea of atoms from Greece to the modern era, one remarkable fact stands out. So long as the atomic theory was not induced from scientific data, it was utterly useless. It explained nothing and integrated nothing. Even in the hands of great scientific geniuses, nothing came of the idea. In the 17th century, both Galileo and Newton also guessed that matter was made of atoms, but the achievements of both men are independent of that guess. In general, belief in atoms was widespread during the scientific revolution, and yet this belief made no significant contribution to the tremendous progress in physics.

This fact should surprise anyone who accepts the standard view of scientific method that is taught today. Students are usually told that scientists start with an arbitrary hypothesis. Objectivity then arises at a later stage when scientists devise experiments to test whether they are lucky guessers. If it turns out that the experiments confirm their guess, then they can allegedly deduce further implications of the idea, which will lead to more experiments, and so on. The atomists’ theory—one of the luckiest guesses in the history of science—appears to be a perfect example of this method in action. Yet the idea turned out to be a dead end: For more than two thousand years, scientists were unable to devise any experiments or to work out any implications based on this theory. It seems that they lost even while hitting the jackpot. Why?

The Greek theory was useless because an idea not derived from observed facts is necessarily isolated from one’s real knowledge. If one tries to think about the implications of such an idea, one simply draws a blank. Implications depend upon connections to the rest of one’s knowledge; an unintegrated idea has no implications. It is therefore impossible to make any predictions or devise any experiments on the basis of such an idea. A scientist who starts with an arbitrary guess will get nowhere, even in the very rare case in which the guess turns out to be correct within a later context of knowledge.

If it is wrong for scientists to start with arbitrary guesses, where should they start? The same place everyone should start: with the evidence directly available to one’s senses. And there is no direct perceptual evidence for the existence of atoms. On the perceptual level, matter appears to be continuous, and this is where we properly begin. At the early stages of science, questions about the ultimate, irreducible properties of matter—including the question of whether it is discrete on some imperceptible scale—do not legitimately arise. The questions that do arise from early observations are challenging enough to keep scientists busy for a long time. Such questions include: How do bodies move? What forces can they exert on each other? How do they change when heated or cooled? Why do objects appear colored, and how is colored light related to ordinary white light? When different substances react, what transformations can they undergo, and under what circumstances?

Over the course of centuries of asking such questions, and painstakingly discovering the methods required to answer them, scientists can and did extend their knowledge further and further from the perceptual level. They slowly built the advanced context of knowledge that eventually made the question of the existence of atoms meaningful and the answer possible. Scientists needed to know an enormous amount before they could hope to transform this idea from an arbitrary claim into real science.

To arrive at the theory, scientists needed Newton’s universal laws of motion, because one cannot work out the implications of the atomic theory without some knowledge of how atoms move. They needed to distinguish between temperature and heat, and to develop methods for measuring both. They needed Lavoisier’s chemistry, particularly the principle of mass conservation and the quantitative method for distinguishing elements from compounds. They even needed the knowledge that led to the invention of the electric battery, which played a key role in the analysis of chemical compounds. And, in addition to all this specific knowledge, they needed the epistemological legacy of two scientific geniuses—Newton and Lavoisier—to show them how to investigate nature.

By the year 1800, after centuries of building higher level generalizations upon earlier knowledge, scientists reached a stage at which they were discovering truths very remote from what is given in direct perception. For instance, they were able to calculate the mass of the sun, to discover a vaccine against smallpox, to make inferences about natural history from fossil records, and to develop the wave theory of light.

It was at this advanced stage of knowledge that the issue of atoms first arose in a scientific context. From the first evidence that matter is composed of atoms to the full proof required only about seventy years. When the idea of atoms arose from observed facts, scientists had a context in which they could think about it, and therefore derive implications, make predictions, and design experiments. The result was a sudden flurry of scientific activity that quickly revealed an enormous depth and range of evidence in favor of the atomic composition of matter.

Of course, goals must be defined rationally before one can achieve them. In this case, the very concept “atom” had to be reformed before scientists had any hope of proving the atomic theory. The concept that emerged from observations differed from the old idea based on deductions from floating abstractions. In Greece, the atom had been defined as the ultimate, immutable, irreducible unit of matter. In the 18th century, Lavoisier pointed out that such a concept was useless because scientists knew nothing about such ultimate particles. Thanks to Lavoisier, what scientists did know about was chemical elements. The new scientific concept that took shape was that of the chemical atom. Gradually, scientists came to understand that an atom had to be defined as the smallest particle of an element that can enter into a chemical combination. The question of whether it is possible to break these chemical atoms into smaller constituents by non-chemical means had to be put aside and left open. With this understanding, the idea of atoms finally referred to something knowable.

By the turn of the 19th century, chemists had identified about two dozen elements and were progressing rapidly in their understanding of how elements combine to form compounds. These investigations gave the first clear support for the idea that matter is composed of atoms. In the early decades of the century, strong evidence accumulated in favor of the view that chemical compounds are specific arrangements of the discrete particles that make up elements.

The first evidence was discovered when chemists studied cases in which two elements combine to form more than one compound. For example, nitrogen and oxygen can combine to form several compounds with very different properties. One of them is a brown gas (NO2), one is a white solid (N2O5), one is a blue liquid at low temperatures (N2O3), and another is a colorless gas that can cause people to burst into hysterical laughter (N2O). All of these substances are made of the same two elements, and yet they are radically different. And when chemists carefully compared the relative weights of nitrogen and oxygen in each of these compounds, they discovered a crucial law of chemistry.

Suppose we start with a sample of laughing gas, and find that it contains 1.75 grams of nitrogen and exactly 1 gram of oxygen. Then we compare samples of the other compounds that contain the same amount of nitrogen. We find that the blue liquid contains exactly 3 grams of oxygen, the brown gas 4 grams, and the white solid 5 grams. In what seems to be a striking coincidence, all the weights are exact integer multiples of the 1 gram of oxygen found in the laughing gas.

John Dalton, the English chemist who discovered this fact, did not believe it was a coincidence. In 1805, after seeing that this same pattern held for compounds of carbon and oxygen, and for compounds of carbon and hydrogen, he announced a general law: When two elements combine to form more than one compound, the weights of one element that combine with identical weights of the other are in simple multiple proportions. And he pointed out that this is precisely what one would expect if elements are composed of atoms with identical weights. A compound can contain one atom of a particular kind, or two, or three, but it cannot contain 3.42 such atoms. So the relative weights of the element in different compounds have to be integer multiples. This discovery was named the law of multiple proportions, and the atomic theory provided a simple explanation of it.

A few years after Dalton published his work, a French chemist named Joseph Louis Gay-Lussac discovered another law that could be understood in terms of atoms. Gay-Lussac found that the volumes of gases involved in a reaction can always be expressed as a ratio of small whole numbers. At a sufficiently high temperature, for example, one liter of oxygen will combine with two liters of hydrogen to give exactly two liters of steam. Or, for instance, one liter of nitrogen will combine with three liters of hydrogen to give exactly two liters of ammonia gas.

Gay-Lussac offered his law merely as an empirical generalization without explanation. In 1811, however, an Italian chemist named Amadeo Avogadro thought of a hypothesis that would explain it: Equal volumes of gases, he reasoned, must contain the same number of particles. If this is true, then the fact that only whole numbers of atoms can combine to form a molecule implies that the ratios of the combining gas volumes must be whole numbers. Therefore the idea of atoms, in combination with Avogadro’s hypothesis, had the power to explain yet another empirical law.

So far, we have considered only cases in which compounds contain different proportions of the same elements. However, chemists soon made another startling discovery: Substances with radically different properties can be made of elements in the same proportions.

Let us start with a simple example, which is not even a compound but a pure element. It was known that the black, chalky substance we call graphite is made of pure carbon. In 1814, Humphry Davy (the English chemist who discovered laughing gas) used an enormous magnifying glass to heat a diamond until it burned and disintegrated. To his amazement, it disintegrated into carbon dust. Davy proved that pencil lead and diamonds are composed of the same stuff. (Inexplicably, however, tests showed that scientists got consistently negative results upon giving their wives graphite jewelry.)

Now consider another case, this one involving a chemical compound. The ethyl alcohol that many of us like to drink is found to consist of two parts carbon, six parts hydrogen, and one part oxygen. Another compound, methyl ether, also contains carbon, hydrogen, and oxygen in the exact same proportions. Yet, when cooled into a liquid state, methyl ether is not at all enjoyable to drink.

Different chemical compounds made of the same elements in identical proportions are called “isomers,” a term that derives from the Greek words meaning “equal parts.” The existence of isomers, which was proven in the 1820s, is easy to understand with the atomic theory and difficult to understand without it. According to the atomic theory, the chemical properties of a molecule are determined by the elements and their arrangement. It is not merely the proportions of elements that are relevant, but also how the elements are put together—that is, which atoms are attached to which other atoms and in what spatial configuration. On the other hand, a continuum theory of matter would seem to imply that the same elements mixed together in the same proportions should always result in the same stuff.

If atoms are everywhere, then chemists should not be the only scientists able to find them. One would expect physicists to contribute to such a fundamental discovery, and they did, particularly when they investigated heat and the physical properties of gases.

Physicists define the property of a material called “specific heat” as the amount of heat required to raise the temperature of one gram of the material by one degree. It was known that the specific heats of different materials vary over a wide range. For example, it requires much more heat to raise the temperature of a pound of aluminum by a given amount than it does to raise the temperature of a pound of lead by the same amount.

In 1819, two French physicists, Pierre Dulong and Alexis Petit, measured the specific heats of thirteen elements and discovered a remarkable relationship. Rather than comparing equal weights of the different materials, they decided to compare samples with equal numbers of atoms. So they simply multiplied the measured specific heats by the relative atomic weights that had been determined recently by the chemists. This simple calculation gives the specific heat for a particular number of atoms, rather than the specific heat for a unit mass.

Amazingly, when Dulong and Petit performed their careful measurements of specific heat and multiplied by the atomic weights, they arrived at the same number for each of their thirteen elements. In other words, they found that equal numbers of atoms absorb equal amounts of heat, independent of the material. This meant that the wide variations in the heat capacities of different bodies can be explained simply by differences in the number of atoms. Another mystery had apparently been solved by the atomic theory.

But this was only the beginning. This discovery raised interesting questions, namely: What is happening when an atom absorbs heat, and why does each atom absorb the same amount on average? A crucial turning point came when the atomic theory could provide the answers. I’ll indicate briefly the reasoning that led to this breakthrough.

Consider someone who vigorously rubs two sticks together in order to start a fire. Somehow the external motion of the sticks is being converted into heat. But Newton’s laws led physicists to expect that energy of motion—called kinetic energy—should be conserved in this case. How can it be conserved if it disappears into heat? One possible answer is: The motion has not disappeared at all; the external, visible motion of the sticks is being converted to an internal, invisible motion of the tiny particles that make up the sticks. According to this idea, the friction between the moving sticks has excited and increased the chaotic, internal motions of the atoms in the sticks—and when we feel the increase in temperature, we are sensing the increase in atomic motion.

One implication of this idea is that there must be a constant conversion factor between external kinetic energy and heat. In other words, a particular amount of motion must always cause the same amount of heat. This was experimentally proven in the 1840s by the English physicist James Joule, and the result supported the interpretation of heat as atomic motion.

At this stage, the idea was intriguing, but not yet convincing; more evidence was needed. The crucial evidence came when someone thought of trying to understand the physical properties of gases in terms of atoms. The first atomic model of gases was very simple. Imagine a few thousand Super Balls flying about a room at high speeds in all directions, bouncing off the walls, the ceiling, the floor, and each other. The balls move freely except at impact, when they change their motion in accordance with Newton’s laws. If you now substitute atoms for Super Balls, you have a physical model of the air in the room.

This simple model led immediately to a basic law relating the pressure, volume, and energy of a gas: The product of the pressure and the volume is proportional to the number of atoms and the average kinetic energy of the atoms. Now recall that there were already reasons for suspecting that the average kinetic energy of the atoms should be interpreted as the temperature of the gas. So the atomic theory implies that the product of the pressure and the volume should be proportional to the temperature. This is the well-known, basic law of gases that had been discovered experimentally by Jacques Charles in 1787. Thus the atomic theory claimed another major victory.

The equation that came from the atomic analysis had further implications. For example, it implied that equal volumes of gases must contain equal numbers of molecules, provided that the pressure and temperature are the same. In other words, the atomic theory of gases explained why Avogadro’s hypothesis must be true. The theory also made clear what is happening when motion is converted into heat and, in addition, why heat is conserved when transferred between bodies. The explanatory power of this one result was astonishing; this was an enormous step toward proving the atomic theory and toward integrating the sciences of physics and chemistry.

By the middle of the 19th century, more evidence for the atomic composition of matter had been discovered. For example, the atomic theory explained the laws of electrolysis discovered by Michael Faraday, which relate the fields of chemistry and electricity. It also provided an explanation for the various types of crystals that had been identified, thereby transforming the whole field of crystallography from a descriptive subject into a causal science. The range of evidence—from chemical reactions to heat capacities to properties of gases to electricity to crystal forms—was extremely impressive.

Now let us consider how this evidence was evaluated by 19th-century scientists. Since the evidence was so abundant and convincing, you might not expect much controversy. After all, facts are facts, and if all the facts point toward the atomic nature of matter, then scientists will surely accept this profound truth and take pride in their discovery of it.

Yet that is not what happened. Consider first the reaction to Dalton’s ideas. One historian of science puts it this way: “Dalton’s theory was not generally treated as an atomic theory, but simply as laws of definite proportions. At first the theory did not arouse much attention at all; and when it did the hypothetical part set many teeth on edge, and was often ignored as an eccentricity.”2 In other words, most chemists merely accepted Dalton’s laws as empirical generalizations, while rejecting his claim that the atomic nature of matter was the underlying cause of the laws. These chemists were not critical of Dalton’s atomic explanation because they thought he lacked sufficient evidence; rather, they simply dismissed atoms as an “eccentricity” that did not belong in a scientific theory.

This attitude was adopted almost unanimously by the authors of chemistry textbooks. For instance, William Brande, the author of a textbook entitled A Manual of Chemistry, wrote: “The theory of definite proportions has been much blended with hypothetical views, but it will be most satisfactorily and usefully considered as an independent collection of facts.”3 Of course, in comparison to a fundamental causal theory, an “independent collection of facts” can only be described as unsatisfactory and useless. But the writers of 19th-century chemistry textbooks disagreed. It was not until very late in the century that one could find chemistry textbooks that discussed the atomic theory.

How did chemists react to the crucial hypothesis of Avogadro? Incredibly, they ignored it for almost fifty years. Like Dalton, Avogadro was out of step with the times. Part of the problem was that he also “set many teeth on edge” with his ideas about atoms. But the full problem went even deeper. Avogadro believed in a physical approach to chemistry in which conclusions were reached by integrating data from chemical reactions with other data available from physicists—for instance, data regarding vapor densities, specific heats, and crystal forms. Most of Avogadro’s colleagues, however, took the view that chemists should stick to chemistry and leave physics to physicists. In other words, they treated chemistry as an autonomous science that dealt only with the rules governing chemical reactions.

This attitude plagued chemistry for much of the 19th century. The correct atomic weights of elements could not be unambiguously determined by data from chemical reactions alone. But many chemists refused to use the other physical data that were needed. As a result, the atomic weights in common use before 1860 were systematically in error. This, in turn, caused errors in determining molecular formulas; for example, water was taken to be HO rather than H2O.

And what happened when the atomic theory of gases was first developed, thereby proving that Avogadro’s hypothesis had to be true? The scientific community had no reaction at all to this landmark discovery—because they did not hear about it. The physicist who made the discovery, J. J. Waterston, presented his work in a brilliant paper that was submitted for publication in 1845. Waterson sent the paper to Philosophical Transactions of the Royal Society, the leading scientific journal in England. But it was never published. The reviewer wrote that “the paper is nothing but nonsense, unfit even for reading before the Society.”4 This was the paper that provided the first correct explanation for the law of gases, for the law of combining volumes, and for the relationship between motion and heat—and yet it was dismissed as nonsense.

Why were the explanations of Dalton, Avogadro, and Waterston shunned and ignored?

To understand the answer, one must recognize that it is the science of philosophy that teaches us how to weigh evidence and reason in accordance with the facts—in short, how to be objective. One must also recognize that different philosophies offer vastly different views of what it means to be objective, or even of whether objectivity is possible or desirable. And, finally, one must bear in mind that the atomic theory had the misfortune of being the first major new scientific theory developed in the post-Kantian era. This last is the key to understanding why the theory of atoms has been opposed or corrupted from its inception two centuries ago.

In the premier issue of this journal, I described the rebellion against reason that occurred in continental Europe at the end of the 18th century. This was one of history’s major turning points: the transition from a Newtonian age to a Kantian one. In the Newtonian age, steady progress toward a fundamental understanding of matter was typically viewed as natural and unproblematic. In the Kantian age, however, the very goal of grasping the underlying nature of external things was widely rejected as impossible. Precisely because the atomic theory was a dramatic triumph of human reason, the Kantian era was committed by its deepest premises to declaring war on it.

Recall that Kant banished reality from the realm of human thought, and replaced it with a delusion called the “phenomenal world,” a world of appearances created by our minds. He referred to reality as the “noumenal world”—the world of “things-in-themselves”—and he insisted that it is unknowable and cognitively irrelevant. He wrote: “What the things-in-themselves may be I do not know, nor do I need to know, since a thing can never come before me except in appearance.”5 According to Kant, we never perceive reality, and reason is powerless to know anything about it. Reason deals only with appearances, that is, with the subjective world of its own creation.

Newton’s followers took it for granted that a scientist’s task is to identify the underlying causes of the way things appear. A cause is the nature of a thing that necessitates its actions. Kant, however, entirely rejected this approach; he claimed that any such cause is unknowable. Science, he insisted, must be confined to the world of appearances, and this implies strict limits on the questions one is allowed to ask. It makes no sense to investigate aspects of the appearances that do not appear, for the simple reason that there are no such aspects. The search for things that underlie and explain the appearances is, according to Kant, based on a false view of causality. On his view, causality is nothing more than an innate rule of the mind that regulates the actions of appearances. There is never any need to explain those actions by reference to any unobserved entities. To the extent that we can speak of explanation at all on the Kantian view, the explanation is merely this: By the nature of our minds, such is the way we create the appearances.

It is no surprise, therefore, that Kant adamantly rejected the atomic theory of matter. “Natural science,” he wrote, “will never reveal to us the internal constitution of things, which, though not appearance, yet can serve as the ultimate ground for explaining appearances. Nor does science need this for its physical explanations. . . . For these explanations must only be grounded upon that which as an object of sense can belong to experience. . . .”6 Since the goal of physics is not to understand the nature of the real world, but only to describe the phenomenal world, there is no place for conjectures about atoms.

Kant’s ideas spread very quickly. Throughout Europe, the intellectual groundwork had been well prepared for them. In France, the failure of Cartesian rationalism eventually caused a swing toward skepticism and finally resulted in Rousseau’s open hostility toward reason and science. In Germany, Kant’s predecessors were Luther, who despised reason, and Leibniz, who made a mockery of it. In England, the modern empiricist philosophy had led Hume to cry out in anguish that he knew nothing, not even where or what he was. This was the perfect atmosphere for the dissemination of Kant’s poison.

Consequently, 19th-century scientists found themselves in a conflict. On the one hand, they inherited the scientific knowledge and rational methods that were passed down from the Age of Reason and the Enlightenment. On the other hand, they were being bombarded from all sides with the new Kantian philosophy. In practice, many scientists continued to go through the motions they had learned from Newton and Lavoisier, and by doing so they discovered new facts and new laws. To the extent that they accepted any form of Kantianism, however, even these scientists were stopped from integrating the new facts into a rational theory. Many other scientists who accepted the Kantian view more consistently were stopped even before they could discover any new laws. The results were devastating. For example, whereas France was the world leader in chemistry at the turn of the century, by mid-century the dominance of the “describe-the-appearances” approach had led to complete stagnation, and no significant new discoveries were coming from the chemistry departments of French universities.

At mid-century, the science of chemistry was in chaos. Most chemists were reluctant to speak of “atomic weights” and instead used the theory-neutral term “equivalents” when referring to the relative weights of elements that combine in chemical reactions. The situation may be summarized as follows: Chemists could not agree on whether to call these crucial numbers “atomic weights” or “equivalents”; they could not agree on the numerical values; and they could not agree on what data should be used to determine the values. Consequently, they could not agree on the proportions of elements that make up compounds. The Kantian chemists who opposed atoms and advocated “equivalents” were using one set of formulas; those who were less hostile toward the idea of atoms were using a different set.

By the late 1850s, an Italian chemist named Stanislao Cannizzaro had lost patience with this situation. He was convinced of three points: first, that chemists needed to accept the existence of atoms; second, that they needed to recognize the truth of Avogadro’s hypothesis; and third, that they needed to use the full range of available data—including data from physicists—to determine one consistent set of atomic weights. Cannizzaro wrote a paper making his argument and showing how to determine the correct atomic weights. He then helped to organize a major meeting of European chemists in Karlsruhe, Germany, at which he tried to persuade his colleagues.

The conference occurred in September of 1860. The most avid of the anti-atomists did not attend because they suspected that the meeting’s purpose was to promote the atomic theory. Even so, Cannizzaro did encounter opposition, which was led by the prominent German chemist Friedrich Kekule. Kekule defended the independence of chemistry from physics, insisting that chemists should base their reasoning solely on data about chemical reactions. As to the existence of atoms, he had this to say: “The question whether atoms exist or not has but little significance from a chemical point of view; its discussion belongs rather to metaphysics. In chemistry, we have only to decide whether the assumption of atoms is a hypothesis adapted to the explanation of chemical phenomena. . . . From a philosophical point of view, I do not believe in the actual existence of atoms. . . .”7

This is a bizarre position that no Enlightenment scientist would ever have taken. But it was a common view in the 19th century. Kantian philosophy told Kekule not to believe in the real existence of atoms, and he obeyed. He regarded the real existence of anything as an issue for metaphysicians to debate and held that scientists must limit themselves to the phenomenal world. Nevertheless, Kekule thought that scientists were allowed to adopt the atomic hypothesis if it was useful in dealing with the phenomena. And he did believe that it was a useful working assumption that the appearances behave as if they are made of atoms.

In practice, Kekule made great use of the atomic theory, and his major discoveries would have been impossible without it. He discovered the atomic structure of benzene, and he was one of the founders of organic chemistry. In his mind, however, the fact that he needed the atomic theory for his work had nothing to do with the allegedly unanswerable question of whether atoms exist in reality.

This Kantian split between thought and reality explains the outcome of the Karlsruhe conference. Cannizzaro won in a limited, practical sense: Within a few years most chemists adopted his recommended atomic weights. But he made far less headway convincing his colleagues of the real existence of atoms.

Meanwhile, new evidence kept accumulating during the 1860s. The field of organic chemistry was progressing rapidly, and the progress was entirely dependent upon thinking in terms of atoms and molecular structure. The new concept “valence” was proving invaluable to chemists, and valence can be understood figuratively as the number of “hooks” an atom has for attaching to other atoms. In addition, physicists were making outstanding progress with the atomic theory of gases. James Clerk Maxwell was able to extend the theory in order to explain the rates of gaseous diffusion and heat conduction. He even made the surprising prediction that the damping of a pendulum due to air friction was independent of air density over a wide range. This result was then confirmed in a series of careful experiments, providing dramatic evidence for the atomic theory.

In 1867, shortly after Maxwell published a landmark paper on the theory of gases, there was a meeting of the Chemical Society in London. The major event at this meeting was a paper by Benjamin Brodie entitled “Ideal Chemistry.” Just as Maxwell was completing the proof of the atomic theory, Brodie offered a new approach to chemistry that entirely rejected atoms. One historian summarizes Brodie’s philosophic view as follows: “The true object of science is not to explain, but to describe. We cannot ask what water is, only what it does, or what it becomes. We have no means of grasping the underlying reality of things, and so should content ourselves with the accurate description of what things
do. . . .”8

How does a chemist avoid referring to the nature of substances and restrict himself to merely describing observable actions and changes? This was the question that Brodie addressed in his presentation. The key to the answer, he claimed, was a new system of classification in chemistry. Brodie proposed a system that treated chemical changes, rather than chemical substances, as primaries. These changes are described by chemical equations that name the amounts of reactants and the amounts of products. For example, two liters of steam can change into one liter of hydrogen and one liter of hydrogen peroxide. Or, for instance, two liters of hydrogen chloride gas can change into one liter of hydrogen and one liter of chlorine.

In Brodie’s theory, substances are not classified in terms of their essential nature, but instead by the number and type of operations required to make them. He implemented this idea by grouping together chemicals that appear in similar places in similar equations. In the two examples above, both hydrogen peroxide and chlorine appear as products along with hydrogen in equations that have the same coefficients. Therefore, according to Brodie, these two substances should be grouped together and designated by similar combinations of symbols. Thus chlorine is represented by symbols that make it appear to be a compound rather than an element.

This is worse than nonsense—it is philosophically malicious nonsense. Brodie was attempting to stop the progress in chemistry that seemed to violate Kant’s dogma that we cannot know “things-in-themselves.” So he devised a new chemical language that deliberately obscured the basic facts about the nature of chemical substances.

When the theory was presented to the Chemical Society in 1867, there were some critical comments. With a touch of sarcasm, Maxwell said that he was surprised to learn that hydrogen and mercury were operations rather than substances. Also, Kekule made it clear that Brodie’s whole system was based on starting points that were chosen arbitrarily, and different choices would have resulted in a different classification scheme. Nevertheless, the reaction to the theory was surprisingly positive. One author notes that “in spite of some criticisms, the tone of all the speakers was respectful, and at times flattering.”9 After the meeting, the journal Chemical News devoted almost a whole issue to Brodie’s theory, calling it “The Chemistry of the Future.” The theory was also praised in the North British Review, which claimed that the atomic theory remained as doubtful as it had been in the days of Lucretius.10

Brodie’s anti-theory was a philosophic and scientific monstrosity. It received a respectful hearing only because there were widespread feelings of distrust and hostility toward atoms. Given the overwhelming scientific evidence in favor of atoms, there was only one source for such feelings. They came from philosophy—primarily from Kant, who was assisted by a long line of philosophers from Heraclitus to Hume.

This hostility became evident at the meeting when Brodie ridiculed the use of atomic models of molecular structure. He read to the audience the following advertisement from a scientific journal: “The fundamental facts of chemical combination may be advantageously symbolized by balls and wires, and those practical students who require tangible demonstration of such facts will learn with pleasure that a set of models for the construction of glyptic formula may now be obtained for a comparatively small sum.”11 This is a perfectly reasonable ad for molecular model kits, which help chemists and students to understand the spatial arrangement of atoms in a molecule. When Brodie read the ad, however, he had to wait for the derisive laughter to subside before continuing. He took for granted that such models were ridiculous, and most of his audience agreed. Brodie then remarked that the ad was clear evidence that chemistry had gotten “upon a wrong track,” a track that was “altogether off the rules of philosophy.”12 His rulebook of philosophy was Kant’s Critique of Pure Reason.

The chemist who had introduced these ball-and-wire molecular models, Edward Frankland, was at the meeting. In the 1850s, Frankland had pioneered the idea of atomic valence, which corresponds in the models to the number of wires that an atom has for attaching to other atoms. For instance, hydrogen atoms have a valence of one and therefore one wire, oxygen has two and carbon four. Frankland had written a textbook entitled Lecture Notes for Chemistry Students, in which he made extensive use of these models in order to explain the nature of compounds in terms of their molecular structure. This was a crucial advance, and the models had already proven to be enormously useful, particularly in organic chemistry.

Yet it was Brodie who received widespread support while he attacked and ridiculed, and it was Frankland who backpedaled while feeling embarrassed and isolated. In his response, Frankland feebly tried to defend his models by saying: “I certainly do not imagine that any evil is likely to arise from such symbolic representations. . . .”13 He then emphasized that he never intended the models as accurate depictions of anything real. He conceded the entire issue with the following confession: “[I do not regard the models as] representations of the position of these atoms in the compound. . . . I cannot do better than state, simply and at once, that I [do not] believe in atoms.”14 When asked why chemists should use the atomic theory, Frankland claimed that the theory serves “as a kind of ladder to assist the chemist in progressing from one position to another in his science.”15 He never explained how a false theory can function as an indispensable means for advancing a science.

To use the atomic theory while denying its truth was a popular option among chemists of this era. One of the chemists at the meeting, William Odling, had made important discoveries about the molecular structure of certain acids and salts; however, he laughed at what he called “Frankland’s marvelous picture book.”16 At the meeting, Odling announced: “[I] do not believe in atoms, and [I] keep the idea of atoms in the background as much as possible.”17 He did not reject atoms in practice; he realized that without the atomic theory he would not be able to do his research. But he kept atoms in the “background” and refused to acknowledge their reality. The logical fallacy that Ayn Rand referred to as “concept-stealing”—using a concept while ignoring or denying a more basic concept on which it logically depends—is petty theft compared to the epistemological crime of Odling and his fellow chemists; they were guilty of “theory-stealing.” This was the contradiction by means of which such chemists accepted Kantian skepticism and nevertheless attempted to continue functioning.

But contradictions do not work in theory or in practice. There was a price paid by chemists who worked with atoms but viewed them as unreal “symbolic representations.” For example, during the 1850s and 60s, these chemists encountered a problem concerning isomers. They wrote their symbolic representations down on paper, and they figured out how many different ways the symbolic atoms could be rearranged. The result, they thought, should correspond to the number of isomers found in the laboratory—but sometimes the actual number of isomers differed from their prediction.

This mystery was solved in the early 1870s by a young Dutch chemist named Jacob van’t Hoff. Evidently, van’t Hoff had escaped Kant’s influence and therefore took the ball-and-wire models seriously. As a result, he was free to recognize what every child knows: In contrast to symbolic representations on paper, balls and wires can be arranged in three dimensions. When van’t Hoff worked out the number of ways that atoms could be rearranged in three-dimensional molecules, he predicted the correct number of isomers.

Van’t Hoff’s correct predictions elicited a predictable response from the anti-atomists. One prominent German chemist, Wilhelm Kolbe, wrote: “The modern chemist, . . . who determines the positions of all the atoms in a compound, has long since abandoned the solid ground of exact science; the scientist has become a metaphysician.”18 He referred to van’t Hoff’s work as “phantasmagorically frivolous puffery” and added: “The prosaic chemical world had no taste for these hallucinations.”19 Kolbe continued to thunder against the atomic theory until his death in 1884.

In France, the controversy over atoms erupted a decade after Brodie’s presentation to the London Chemical Society. In 1877, at a meeting of the Paris Academy of Sciences, Marcellin Berthelot squared off against Adolphe Wurtz. Both were prominent chemists; Wurtz was one of the few vocal advocates of the atomic theory in France, and Berthelot was a passionate opponent of the theory. After Wurtz cited the evidence and presented his arguments, Berthelot responded with his famous rhetorical question: “Who has ever seen a gaseous molecule or an atom?”20 He then declared: “The only thing [the atomic theory] has done has been to intermix the meshes of its hypotheses with our demonstrated laws, and this to the great detriment of the teaching of positive science.”21

Berthelot had two effective weapons to use in his battle against Wurtz and the atomic theory. First, he had the support of post-Kantian philosophy, which enabled him to seize the intellectual high ground while sneering at Wurtz’s old-fashioned ideas about causality and explanation. Second, Berthelot held a political position that gave him enormous influence over what was taught in French universities. Both the hiring of faculty and the curriculum at French universities were controlled by the “Superior Council of Public Instruction,” and Berthelot served on the Council as the leading voice on matters of science education. In this capacity, Berthelot had the power to prevent advocates of the atomic theory from receiving faculty positions, and he sometimes used that power.22

Regarding the issue of whether French chemists should continue to use “equivalents” or switch to atomic weights, one chemist made the following observation at the meeting: “[S]uch an important change as the introduction of a system of chemical notation can only be generally introduced when it has been judged necessary, not only by the majority of teachers, but also by the Superior Councils which govern the University, and in these chemists are not the only persons to have influence.”23 And, he could have added, such a change would never be approved so long as Berthelot was on the Council. Berthelot did what he could to make sure that French chemistry stagnated at the level of empirical laws and never advanced to a fundamental causal theory. The council on which he served was like the Council of Scholars in Ayn Rand’s novelette Anthem, which approved of candles but opposed electric lights.

The pitiful state of French science is best illustrated by a conversation Berthelot had with another chemist in the mid 1880s. While explaining why he crusaded against the atomic theory, Berthelot declared: “I do not want chemistry to degenerate into a religion; I do not want the chemist to believe in the existence of atoms as the Christian believes in the presence of Christ in the communion wafer.”24 His colleague told him not to worry; after all, he reassured Berthelot, atoms are only a mental aid, and nobody believes in their actual existence.

By the 1880s, the evidence for the atomic composition of matter exceeded any reasonable standard of proof. Rejecting atoms was akin to rejecting the heliocentric theory of the solar system. The atomic theory had integrated and explained the fields of chemistry, crystallography, gas theory, thermodynamics, electrolysis, and so on. But none of that meant anything to Berthelot. There was only one form of evidence that he would accept: The atomists would have to present him with an atom that he could hold in his hand and look at. In the absence of such an “appearance,” he insisted that accepting the existence of atoms was an act of blind faith.

Kant introduced many complicated contortions in order to destroy people’s confidence in reason, and thereby reduce scientists to this state. But the state itself is simple. Kant’s mission was accomplished when people accepted the false alternative between acts of blank staring and acts of blind faith. Then the clocks were turned back, the image of the scientist was erased from men’s minds, and people were left with the choice between the perceptual-level brute who shuns abstractions and the other-worldly mystic who shuns percepts.

The Kantian assault on the atomic theory continued throughout the 19th century. At the turn of the 20th century, influential scientists across Europe still denied the existence of atoms. There was Karl Pearson in England, Henri Poincare and Pierre Duhem in France, Wilhelm Ostwald and Georg Helm in Germany, Ernst Mach in Austria, and their many followers. They were like members of a “flat-Earth society,” except they held prominent university positions and were published in prestigious journals.

Eventually, the anti-atomists died or gave up their crusade. Mach lasted the longest; he fought against the atomic theory until his death in 1916. But even when most scientists conceded the existence of atoms, this did not signal the return of rational science. In 20th-century quantum theory, atoms were accepted pragmatically and then banished to a halfway house between reality and unreality, where they remain to this day. That chapter of the story is beyond the scope of this article.

The scientific theory of atoms began with the work of Dalton and is now more than two hundred years old. The discovery of this fundamental knowledge—so far removed from what is accessible to our senses—is one of the greatest achievements in the history of science. But it is an achievement that is in basic conflict with post-Kantian philosophy, and therefore it has been attacked and undercut for two centuries.

Atoms can be defended only on a philosophic foundation that fully accepts the reality of the external world and the efficacy of man’s conceptual faculty. An empiricist epistemology, which merely attempts to describe “appearances,” can never reach knowledge of atoms. A rationalist epistemology, which shuns the senses and builds a dream world out of empty abstractions, can never know them either. Yet this was the choice offered by modern philosophy.

Another alternative has been offered by Ayn Rand. She swept aside these errors and made a fresh start. According to her view, philosophy is the science that defines the proper relationship between a man’s mind and reality. Given this approach, the term “post-Kantian philosophy” is really a misnomer. Kant denied that there is any relationship between human consciousness and reality. The work of those who follow Kant can be described in various colorful ways—but whatever it is they are doing, it is not properly called philosophy. Kant murdered philosophy; the intellectual gyrations of his followers are merely the death throes.

Now, however, the science of fundamental ideas has been reclaimed and reborn. Ayn Rand has identified the nature of concepts, which are man’s basic means of knowing reality. This historic achievement has provided the foundation for a new epistemology. Upon that foundation, Leonard Peikoff has built a theory of induction that provides answers to questions that modern pseudo-philosophers long ago gave up asking. He has described how we start from first-level generalizations and proceed step-by-step to the most abstract scientific theories; in other words, he has explicitly identified the epistemological method by which we acquire knowledge of such things as atoms. I am currently writing a book, Induction in Physics and Philosophy, that will present this theory.

In the history of the “19th-century atomic war,” we have seen the destructive power of corrupt philosophy. But the dependence of physics on philosophy cuts both ways. Whereas the wrong philosophic ideas block the road to scientific progress, it is equally true that the right philosophic ideas pave the way for scientific advancement. I think there is hope that future generations of physicists will grasp that philosophy is a crucial science that can provide them with the rational guidance they need. Then the atomic theory can make a full recovery from its present state of illness and finally achieve its rightful status as a monument to the human mind.

About David Harriman

Mr. Harriman is the editor of Journals of Ayn Rand and a senior writer for the Ayn Rand Institute. He has worked as a physicist for the U.S. Department of Defense and he has taught philosophy at California State University San Bernadino. He has lectured extensively on the history and philosophy of physics. He is currently writing two books: one demonstrating the influence of philosophy on modern physics (The Anti-Copernican Revolution), and another presenting Dr. Leonard Peikoff’s theory of induction (The Inductive Method in Physics).

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