These are the starting lines of Kurd Lasswitz’s short story "On the Soap Bubble," written in 1887. Lasswitz, known as the father of science fiction literature, describes in his short story how a soap bubble becomes the world of his protagonists. Through the soap bubble, they discover the system of science and the establishment of knowledge. Interference colors were common knowledge for Uncle Wendel, as well as for the average nineteenth-century reader. But they had first to be discovered in the seventeenth century and then to be established in the eighteenth. Experimental practice gave way to this physical finding, as well as its demonstration and distribution.

This essay questions the role of painting in translating experimental practice from the realm of natural sciences to the realm of art. It offers a close reading of Chardin’s painting Soap Bubbles as an epistemic device in the face of Newton’s theory of light and color.¹

The use of experiments to discover nature and to verify awareness was set in motion by the text Novum Organum Scientiarum. This book was written and published by Francis Bacon in 1620. In it, the author defines experimental practice as follows: focusing on the research object that leads to its persistent and exact observation;² exerting an influence on the research object in the form of an experimental arrangement;³ as well as the willingness to great stamina and patience to approach step by step an overview over all the natural phenomena without skipping important interstages.⁴ After taking these steps the acquired experiences could be categorized by reason and thus become new knowledge. Opposing the conventional science of his time, which focused only on reason and imagination, Bacon advocated methods closely linked to the phenomena themselves: experiment, trial, manipulation and observation (i.e. the use of the senses) could resolve secrets of nature which reason alone could never find.⁵

To investigate the secrets of light, Isaac Newton used the very values and skills named by Bacon. For forty years, he experimented patiently with the appearance and diversification of white light by leading a beam of light into a darkened room and breaking it down through prisms and mirrors. His instruments to manipulate the beam of light were at first prisms and mirrors, but the process of observation goes by way of the eyes. The findings of his experiment were for the first time published in the Philosophical Transactions of the Royal Society in February of 1671/72. Under the title New Theory on Light and Colors, Newton summarizes his ground-breaking findings. He writes:

It can be no longer disputed whither there be colours in the dark, nor whither they be the qualityes of the objects wee see, nor perhaps whether light be a bodie. For since colours are qualityes of light, having its rayes for their entire & imediate subject, how can wee think those rayes qualityes also, unlesse one quality may be the subject of & sustain another, which in effect is to call it substance.⁶

Hence, light is a “Heterogeneous mixture of differently refrangible rayes.”⁷

This conclusion raised a great deal of criticism.⁸ The public discussions and rejections of the theory of light precluded Newton from issuing further publications. A year after the passing in 1703 of Robert Hooke, one of Newton’s strongest disputants, Newton published his famous book Opticks in two volumes.⁹ After forty years of hard work and hundreds of light experiments, he recapitulated and extended his findings about the refrangibility of white light into its colorful components. The assembled formulas, observations, and experiments in his Opticks comprised the foundation for the knowledge of interference colors, which are named in the nineteenth century by uncle Wendel as the cause of the soap bubble’s colorful appearance.

The soap bubble plays an important role in Newton’s theory. The French man of letters Voltaire, who is significantly responsible for the distribution of Newton’s theory on lights in France, wrote in his popular book Elements of Sir Isaac Newton’s Philosophy, published in 1738, that nothing is too small for the philosopher, such that even the smallest soap bubble is a worthy subject of meditation for him.¹⁰ Thus Newton retains in his "18th Observation" in the Opticks:

Because the Colours of these Bubbles were more extended and lively than those of the Air thinn’d between two Glasses, and so more easy to be distinguish’d, I shall here give you a farther description of their order, as they were observ’d in viewing them by Reflexion of the Skies when of a white Colour, whilst a black substance was placed behind the Bubble. And they were these, red, blue; red, blue; red, blue; red, green; red, yellow, green, and so forth.¹¹

The sequence of the colors depends on the thickness of the soap bubble film. The color value arises depending on the different refrangibility of the colors. However, Newton made another observation while experimenting with the bubble. In his "20th Observation" he writes that

the Bubble, by transmitted Light, appear’d of a contrary Colour to that, which it exhibited by Reflexion. Thus when the Bubble being look’d on by the Light of the Clouds reflected from it, seemed red at its apparent Circumference, if the Clouds at the same time, or immediately after, were view’d through it, the Colour at its Circumference would be blue. And, on the contrary, when by reflected Light it appeared blue, it would appear red by transmitted Light.¹²

Hence, the bubble appears according to the time flow and in relation to the light source in the colors blue or red. This observation clarifies the variance of the colorful emergence, and proves that the colors we notice are not bound to the objects themselves, but to the light.

Newton’s findings were initially subjected to much criticism, but by the beginning of the eighteenth century they established themselves as a new and true discovery. It was the implementation of experimentation as a practice of generating evidence that helped his ideas get accepted. Experimentation not only allowed Newton to investigate light, it also allowed lecturers to demonstrate scientific knowledge and better impart it to their audience.¹³ Newton’s findings were brought to the public not only through scientific publications, but also through popular scientific writings, through public readings and public experimental spectacles.

It was in particular due to the French academic Étienne-François Geoffroy that the Opticks reached the French population.¹⁴ He was an associated member of the Royal Society and had mastered the English language; hence he could translate the Opticks in all details into French. In the time between August 1705 and January 1706, Geoffroy introduced the Opticks to the members of the Académie Royale des Sciences in Paris. Many other scholars visited his lectures, but the lay public had also the possibility to get to know Newton’s theory. Voltaire targeted the lay audience with his mentioned book. Also, the Italian Count Francesco Algarotti intended to enlighten the lay public with his text Il Newtonianismo per le dame,¹⁵ which was translated and published very quickly in French. Thus, the interference colors defined by Newton were distributed through publications by a variety of protagonists all over Europe.

On September 6, 1739, an exhibition opened in the Salon Carré in the Palais du Louvre. For one month, the audience was able to take a look at the works of the members of the Académie Royale des Peinture et Sculpture. Next to paintings by Jean-Baptiste Oudry, Charles André van Loo, and Nicolas Lancret, they could also see the painting Soap Bubbles by Jean Siméon Chardin (Figure 1). This painting was announced in the accompanying catalogue with the words, “Un petit Tableau, représentant l’amusement frivole d’un jeune homme, faisant des bouteilles de savon:” A small painting, representing the frivolous fun of a young man making soap bubbles.

The painting recalls baroque representations of transience. In the tradition of the Homo Bulla (the human as a bubble), the painting shows the finiteness of life through the combination of childhood and the ephemeral soap bubble. Following the emblematic 1594 engraving by the Dutch artist Hendrick Goltzius Quis evadet? (Who can escape?), the motive visualizes not only transience in general but also the finiteness of the beholder’s life. That was also the contemporary interpretation of paintings showing children and soap bubbles.

But if we bear in mind that Newton defines the soap bubble as a scientific device, then another way of interpreting the painting becomes possible. In the following, I shall prove the visualization of a scientific idea — the presence of interference colors — through the painting.

Close observation of the painting brings one to discover two color lines (Figure 2): next to the glass of soap liquid, a red and a blue color line can be seen. They seem to have no function. They are just lying there on the stony window ledge. But these two colors are very meaningful in the context of Newtonian theory of light. They mark the highest and lowest refrangibility of the tristimulus value of the spectrum. Also, the opaque liquid in the glass itself evokes a reminiscence to Newton’s experiments in the dark room: within the glass the beholder can observe a triangular form, which is made prominent by its brighter white. This form brings to mind the triangular prisms Newton used to break the light beam, which he led into the darkened room. The same thing happens here: the white light impinges on the glass, which acts as a prism, it breaks and therefore all the colors within the white beam of light should become visible. But instead of showing all different colors of the rainbow, Chardin chose to paint the highest (red) and the lowest (blue) refrangible colors, which re-mark the endings of the color spectrum and thus stand pars pro toto for all the colors of light.

Above that, the colors red and blue are also very important in conjunction with the observation of soap bubbles. They appear as complementary guises of the bubble. If red, for instance, is the color of appearance in translucent light, the same bubble will turn blue when it is illuminated by reflected light and vice versa. In his Soap Bubbles, Chardin specifically shows reflected light, accompanied by a blue coloring of the bubble. Nevertheless, he also shows the possibility that the soap bubble might turn into red coloring under translucent light. Within the meaning of the metaphor of homo bulla — man as bubble — the tear in the jacket sleeve of the bubble blower establishes a relation with the soap bubble. The tear brings out the white shirt. This representation shows a parallel with the expanding soap bubble. In addition to this, the semi-circular form of the shoulder underlines the comparability of the bubble blower’s body to the soap bubble. The shoulder joint supplements the semi-circular form so that it becomes as round as the bubble itself. Besides that, it is evident that the tear doesn’t only show an opening, but also a little end of the red lining of the jacket. The red color can be seen on the upper right side of the round form. By observing the actual soap bubble, the blue coloring can be located on the opposite side, e.g. on the upper left part of the soap bubble.

In due consideration of these observations, Newton’s explanatory notes on the coloring of a soap bubble can be detected in the painting of Chardin as well. The latter shows the possibility of appearing in red or blue according to time and to the positioning of the illuminating light source. Hence the actual soap bubble gleams in blue and its complementary pendant emerges in the extract of the bubble blower’s body and clothes. This parallelization stems from a formal-aesthetic ordering: the bubble and the shoulder share the same form and perspective. But it also results from a new way of using the traditional representation of the vanitas. The temporally determined progression of the potential colorings on the soap bubble can thus be transferred into the frozen medium of painting. The soap bubble is presented in both color conditions, but not by painting two bubbles or showing both colors in one. Within the painting, red and blue are equally present: one of them on the bubble and the other one on the homo bulla.

These colorful potentialities of the soap bubble are readapted in a further element of the painting: in the two lines of color mentioned before. Since these lines are positioned next to the liquid-filled glass, their presence shifts the possible coloring of the bubble before its actual genesis. Therefore, these two colors are defined as basal features of a soap bubble; it appears that the reference to Newton’s "20th Observation" can be seen in Chardin’s painting.

This described connection between the history of optics and Chardin’s painting complicates the iconographic interpretation of the soap bubble as a symbol of transience. Therefore, the soap bubble does not only represent transience, but also becomes an epistemic device. Consequently, Chardin manages to place the symbol of vanitas in his painting and at the same time to invest it with another meaning: it also becomes a symbol of veritas. Visualizing a scientific awareness in a painting, in this case showing the interference colors, is the result of a combination of traditional representation and effective scientific knowledge. Hence, Chardin’s painting also participates in the diffusion of the Newtonian theory of light and colors. The same beholder who was aware of these findings would also be able to recognize Newton’s interference colors of the soap bubble within Chardin’s painting. Its scientific content was reproduced through the unity of traditional representation and the intentional use of colors, yet scientific practice itself seems to be left out. We only see a young man making a big soap bubble — how could it be an experiment?

To answer this question, we need to take a look at how the experiment came into operation as a method for generating knowledge. At the beginning of the seventeenth century, in his above-mentioned study, Bacon tried to establish experimental practice as a scientific activity by stating that scientists must revoke what they already know and seek insights about their research objects solely through a correlation of observation and experimental setup. ¹⁶ Reason and imagination must be complemented by experience. This new mode of producing knowledge inflects Newtonian research of light. Hence, the use of experiments was supposed to enlighten knowledge by creating new contexts. This approach was also used for a transfer of knowledge to a lay audience. In the following we shall see how it took place and how it related to the game with soap bubbles as an experience and hence as an experiment.

The Enlightenment was a time of striving for greater dissemination of knowledge beyond scientific institutions. ¹⁷ Since the second half of the seventeenth century, an increasing number of publications aimed to distribute scientific problems in a witty and accessible manner. Those writings prepared their (often lay) readers and enabled them to participate in scientific conversations that were common in the salons or at social occasions. ¹⁸

As a consequence, more and more scholars endeavored to spread knowledge not only by written publications but also through public experiments. In the cause of this attempt to popularize knowledge, which combined entertainment and the economic benefit of scientific findings, the formally closed doors of academies and laboratories were opened. The lay public was invited to see the wonders of nature with their own eyes.

The French theologian Marin Mersenne pleaded for a new public space for scientific discourse that would exist alongside academic institutions. Mersenne organized public evening talks, the so-called Conférences, in his Parisian apartment that combined experiment and lecture. ¹⁹

These Conférences were very popular, and other scientists soon followed his example. The French physicist and philosopher Jacques Rohault, for example, held his own Conférences every Wednesday, in which he visualized scientific topics like colors, light, air pressure, and the vacuum through demonstration and explanation. ²⁰ The way in which he playfully revealed the mechanisms of nature resembled a theatrical performance. ²¹ The curiosity of the audience was met because the experiments surprised and amazed spectators without losing their educational character. ²² Furthermore, the laymen should be animated to copy the seen experiments. In his Elements of Sir Isaac Newton’s Philosophy, Voltaire points out that Newton himself would have said: “Don’t believe me; believe only your Eyes, and the Mathematicks.” ²³ This statement underlines the request to invite the reader to make his own experiments. ²⁴ By doing so, laymen could retrace scientific findings and understand theoretical explanations.

Despite these demonstrations directly involving the audience by addressing their senses, the spectators themselves remained passive. They experienced knowledge with their perceptual apparatus, but they did not take an active part in the demonstrations. Popular scientific publications, however, constantly called upon their readers to become active themselves. Detailed descriptions and engravings were supposed to encourage readers to carry out their own experiments. Not only the readers of these publications, but also the spectators of public demonstrations of different experiments were invited to reproduce and review the findings in their everyday life, at work, in their households, and even in child’s play. ²⁵

In 1721, the German philosopher Christian Wolff, author of the educational book Allerhand nützliche Versuche (All kinds of usefull trails), wrote that a perfect execution of experiments is based on the reconstruction and repetition of formally conducted experiments. ²⁶ He aimed at leading his readers to make their own experiments and to become able to interpret the discovered and observed findings for themselves. Thus, he highlighted experience as a fundamental approximation to the secrets of nature. In a following step, the observations and experiences should then be integrated by reason. In the same manner, Voltaire also defined the senses as a main access to the world. The senses, however, must be complemented by thought. ²⁷ Only if they are read and interpreted correctly do experiences enable people to critically review popular science publications, demonstrations, and nature itself to eventually acquire knowledge. ²⁸

In fathoming the elements and phenomena of nature, a certain sequence of four successive sections can be identified: 1.) The senses provide the data that is given to human perception; 2.) Attention enables any particular sense to be concentrated on the elements of nature; 3.) Experience helps to contextualize acquired data; and 4.) Trial enhances sensual capacities through using instruments, generating new contexts or focusing on a certain problem, thus visualizing aspects that were not perceptible before.

Popular scientific writings for laymen, as well as scientific demonstrations, did not only serve to disseminate scientific content, but also to depict a new method: the experimental exploration of nature. Experiments became part of domestic practices and provided everyone with the possibilities to conduct trails themselves. Thus, even everyday activities and games gained epistemic potential. According to this, the soap bubble blower isn’t satisfied with the emotional aspect of the beauty of the soap bubble, but inquires into the fragile object. Just like the scholars in their experiments, laymen assumed the role of the researcher and gathered their own knowledge about nature through acting and understanding.

After examining the experimental culture from which it derived, the question of the experimenter in Chardin’s painting can be positively answered: Chardin’s soap bubble blower can by all means be seen as an experimenting layman. If he does understand his activity as a trial, he does no longer consider it as a play, but as a way to gain knowledge about this object. With regard to the research of the light, the soap bubble blower is able to discover that the colors of the soap bubble’s surface vary depending on the strength of its membrane and the angle in which the light falls on it.

The foundation of such awareness is the ongoing repetition of the trial that brings reference values from which general principles can be derived. This ongoing repetition becomes evident in the title chosen for the painting, Les Bouteilles des Savon, ²⁹ namely the plural form Soap Bubbles. Another hint is the compositional accordance of the soap liquid glass and the emerging soap bubble: the straw in the vessel is placed exactly in the same angle as is the straw in the hand of the soap bubble blower. This compositional parallel implies a cyclical activity, suggesting that a new soap bubble will follow after the first one inevitably bursts. Not the end of the soap bubble’s life, but the bubble’s rebirth. In this interpretation the iconographic meaning of the soap bubble as a symbol of vanitas is loosened and opposed by the potential reproduction of the soap bubble. The painting depicts not only the fugacity of life, but also the epistemic potential of the ephemeral shape in a repetitive trial. Observing this fragile object within a trial permits conjecture about its formation, its composition and its influence of the incident light.

The experiment with the soap bubble provides insights about the soap bubble itself, as well as about the white light and its inherent mixture of colors, and it makes them experienceable and verifiable. But the benefit of self-conducted experiments lies above the experience of science also in an immediate self-awareness. For a successful experiment with soap bubbles it is of utmost importance that the blowing person succeeds in creating a soap bubble with the help of the straw split at one end. He must therefore take care, as evenly as possible, not to bring too much air into the bubble while a visual spectacle takes place before his eyes. Relaxed and with a concentrated expression, the blower focuses on the bubble as well as on his own activity. He must proceed calmly and attentively so that the fragile object does not burst. Therefore, he uses his left-hand to hold on to the windowsill and stabilize the body whilst the right-hand rests on top of it holding the straw in place. He has to be patient. During this experiment he has to learn to control his breathing in order to be able to produce a bubble out of the lye for subsequent observation. Hence, the experimental setting empowers the experimenter to get a glimpse behind the surface of things, but it also reflects the active subject in the process of observation and leads their view to themselves. Consequently, as Olaf Breidbach puts it: “Nicht die Natur ist uns unmittelbar: Wir, in unserem Naturerfahren, sind uns unmittelbar.” ³⁰ Nature is not itself immediate, but we ourselves rather become the object of observation in our experience of nature.

To bring the previous thoughts together, it is useful to define the term experiment in its French pendant: experience. While the experiment as postulated by Bacon solely serves the research and examination of natural phenomena, experience combines the subject and the object of a set examination. The conductor of experiments is present in the experimental setting through his individual constitution, his personal anticipation and his inherent connection with the research object. In conclusion, experiments open our eyes, they show us the secrets of nature, but furthermore they reflect our perception and thus become a mirror in which we can ultimately see ourselves.