Reading up on the Opticks. Refashioning Newton’s Theories of Light and Colors in Eighteenth-Century Textbooks Fokko Jan Dijksterhuis University of Twente, Netherlands Robert Smith’s A Compleat System of Opticks (1738) was the most promi- nent eighteenth-century text-book account of Newton’s optics. By rearranging the ªndings and conclusions of Opticks, it made them accessible to a wider public and at the same time refashioned Newton’s optics into a renewed sci- ence of optics. In this process, the optical parts of Principia were integrated, thus blending the experimental inferences and mechanistic hypotheses that Newton had carefully separated. The Compleat System was not isolated in its refashioning of Newton’s optics. Dutch and English promoters of the new philosophy had preceded Smith by giving Opticks a text-book treatment, and they too integrated experimental and mechanistic inferences. In this way eighteenth-century text-books produced a natural philosophical discourse of light, colors and matter. This paper traces the refashioning of Newton’s optics in Dutch and English text-books of natural philosophy during the ªrst half of the eighteenth century. It concludes with the Dutch translation of A Compleat System of Opticks and its reception among innovators of telescope manufacture. The eighteenth century was the age of Newton. Whether or not one agreed with his views of nature and the way to study her, one had to con- front Sir Isaac’s teachings. Those teachings were not always easy. The Principia in particular was a tough study. The age of Newton thus began with teachers unlocking and explaining Newton’s natural philosophy. Al- though Opticks was far more accessible than Principia, Newton’s theories of light and colors were also refashioned for enlightened readers. The Dutch promoters of Newtonianism were the ªrst to give Opticks a textbook treat- ment, integrating it in their expositions of Newtonian natural philosophy. In A Compleat System of Opticks (1738), Robert Smith devoted exclusive at- Perspectives on Science 2008, vol. 16, no. 4 ©2008 by The Massachusetts Institute of Technology 309 Downloaded from http://www.mitpressjournals.org/doi/pdf/10.1162/posc.2008.16.4.309 by guest on 30 September 2021 310 Reading up on the Opticks tention to optics and the Opticks. Yet, Smith too integrated elements of Newton’s natural philosophy beyond the Opticks. And he too, refashioned Newton’s theories of light and colors to meet the needs of didactics. This paper discusses the rearrangements of the Opticks in eighteenth-century textbooks. Smith’s Compleat System will be the centerpiece, as it was the standard text-book on optics of the eighteenth century and beyond. The Dutch reception of Newton’s theories of light and colors provides a pre- lude and a gigue, but here too Smith plays ªrst violin. Textbooks are important in the history of science. They show how new developments were given a place in, and gave form to the established con- ception of the sciences.1 In the case of eighteenth-century optics this is particularly interesting. In the preceding century, the mathematical sci- ence of optics had undergone a paradigmatic change. At the beginning of the seventeenth century ‘optica’ was a branch of mixed mathematics ana- lyzing the behaviour of light rays and the intricacies of perception. In the work of Descartes, Huygens and Newton a new approach to optics devel- oped in which the focus shifted to questions of the nature of light and the explanation of its behaviour. Huygens’ Traité de la lumière (1690) and Newton’s Opticks (1704) accentuated this shift towards physical optics be- cause both omitted the greater part of their writings on geometrical optics from these works. The old ‘optica’ did not, however, disappear and at the turn of the century the question was open as to what the science of optics would look like, how its physical, geometrical, as well as instrumental parts were ordered and mutually related. Eighteenth-century textbooks reveal what the new optics looked like after the seventeenth-century re- shufºing. This paper is conªned to the physical part of optics. The history of geometrical and instrumental optics is exciting and has still been stud- ied insufªciently, but on the occasion of assessing the legacy of Newton’s Opticks it has to be left aside. Prelude: Opticks for the Dutch As is well known, the Dutch were the ªrst, and most effective, promoters of Newtonian natural philosophy on the continent (Feingold 2004, pp. 68–75).2 Willem Jacob ‘s Gravesande (1688–1742) was the ªrst to in- corporate Newtonian philosophy in his lessons when he became professor of mathematics and astronomy at Leiden in 1717 (Berkel 1999a, p. 72). He had served on a diplomatic delegation to England in 1715, where he 1. I am using the term ‘textbook’ in a broad sense, indicating books explaining and making accessible bodies of natural philosophy and mathematics to initiates and non- experts. It applies not only to books used in an educational setting but also to those in- tended for a general audience. 2. For the reception of Newton’s optics in Germany see Hakfoort 1995, pp. 19–26. Downloaded from http://www.mitpressjournals.org/doi/pdf/10.1162/posc.2008.16.4.309 by guest on 30 September 2021 Perspectives on Science 311 became acquainted with Newton, Desaguliers and Keill and had been deeply impressed with the new natural philosophy (Helden 1999, p. 450). ‘s Gravesande’s Physices Elementa (1720) was the reºection of his lectures at Leiden university and was one of the most important textbooks of Newto- nian natural philosophy. It went through numerous editions and transla- tions. ‘s Gravesande treated the physics of light in a rather cursory way, emphasizing the experimental foundations of his claims and preferring a phenomenological treatment. The contents and organization of the book show that ‘s Gravesande was led by didactic considerations of conceptual clarity. Thus, he ªrst treated inºection of light to show the attraction of matter on light rays, and then discussed refraction prior to reºection (Gravesande 1720, 2: book 5, part 1–3). Likewise he opened the part on colors with a discussion of opacity, arguing that it arose from the conªg- uration of essentially transparent particles of any body. Such deviations from the usual order of optical topics show that ‘s Gravesande organized his argument around what he considered the heart of the matter: the physicomathematics of the interaction of light and matter. By way of ‘in- troduction to Newtonian philosophy’ this might seem surprising, as New- ton had always been very careful to separate experimental results from mechanistic hypotheses, but it merely shows the way in which ‘s Grave- sande transformed Newton’s achievements. He introduced the cornerstone of Opticks, different refrangibility, in the context of the colors of bodies, which Newton only discussed as part of his account of the nature of colors (Gravesande 1720, 2: book 5, part 4, chapters 19–20). In the third edition of 1742 of Physices Elementa, ‘s Gravesande elaborated a sophisticated adap- tation of Newton’s theory of colored bodies. (Gravesande 1742, 2: book 5, part 4, chapter 26; Shapiro 1993, pp. 228–229). He attributed colors to both the thickness and the refractive force of the intermediate parts of bodies, building on a detailed rendition of Newton’s observations of the colors of thin ªlms. ‘s Gravesande’s argument was mainly phenomenolog- ical and he did not draw upon his previous account of refraction in terms of attractive forces to explain different refrangibility. At the time ‘s Gravesande began teaching Newtonian philosophy, Dan- iël Gabriël Fahrenheit (1686–1738) was giving public lectures on optics, hydrostatics and chemistry. His primary interest was instruments, of which he discussed several innovations of his own. He discussed a reºector made with steel mirrors he had devised after having read Newton’s com- plaints in Opticks about the difªculties with making good and durable mirrors (Ploos van Amstel 1718, f. 52r). He was much taken by Newton’s design, not so much because of the solution of chromatic aberration— which he considered to be limited—but because of the possibilities of shortening telescopes (Ploos van Amstel 1718, f. 34v). Fahrenheit’s argu- Downloaded from http://www.mitpressjournals.org/doi/pdf/10.1162/posc.2008.16.4.309 by guest on 30 September 2021 312 Reading up on the Opticks ment was primarily experimental, and he refrained from causal expositions after an initial consideration of the nature of light. This revealed his chem- ical bias, identifying light with luminescent phenomena of vacuum globes and exotic substances. Taking a non-committal position regarding the na- ture of light, he tended to a Cartesian conception and attributed light to the second element (Ploos van Amstel 1718, f. 6r). ‘s Gravesande was probably instrumental in the trip John Theophilus Desaguliers (1683–1744) made to Holland in 1729–1730, where he lec- tured in Middelburg, The Hague, and Rotterdam (Berkel 1999a, pp. 80– 81). An anonymous listener made notes, elaborated and published them, providing a brief introduction into experimental philosophy “. which from its most prominent promoter, the outstanding Sir Isaac Newton, not improperly takes the name Newtonian” (Desaguliers 1732, preface).3 The lessons on optics introduced light as a corporeal substance, rejecting wave conceptions, and explained refraction by an attractive force of the me- dium. The exposition was straightforward, purely qualitative, and em- ployed some simple experiments and observations. Colors were introduced in terms of the different refrangibility revealed by prisms and the author claimed that these showed light rays to consist of seven different kinds. The variety of the refraction is certainly caused because the one ray of this kind of light particles being bigger than the other, and propagated with the same speed, has more quantity of motion as the other, and therefore cannot be dispersed from its path so easily (Desaguliers 1732, p.