Louis Bertrand Castel

Jean-Jacques Dortous de Mairan (1678-1771) was accused by d'Alembert of attempting to rehabilitate abstract metaphysical systems. However, Mairan makes clear in his preface to the Dissertation sur la glace (1749) that he distinguishes between good and bad systems. In this he takes a position which differs little from that of Condillac, whom d’Alembert so much admired. An examination of his published works and unpublished correspondence corro-borates this and reveals a sophisticated and in some ways modern conception of scientific method. It seems likely that Mairan’s pronouncements on systems were received with suspicion because of his reputation as a stubborn Cartesian.

This chapter outlines the unique aesthetics of German philosopher Johann Gottfried Herder (1744–1803) by paying attention to his remarks on the “color harpsichord”. “Color harpsichord” is a curious instrument invented by French Jesuit Louis-Bertrand Castel (1688–1757), inspired by the correlation theory between spectral hues and musical scale which English natural scientist Isaac Newton (1642–1726) proposed in Opticks (1704). So Castel attempted to visualize this correspondence between spectrum and musical scale by conceiving an instrument that, on striking a key, shows a color corresponding to the musical note. This color harpsichord was discussed heatedly by many great philosophers of the time (Rousseau, Diderot, Goethe etc.). Herder is among them the one who was most interested in (mentioned most times) the color harpsichord, though anytime negatively. He took the failure of the color harpsichord because of lack of doubt or reflection on sight and hearing being modally different and forces an unnatural mode of perception in reverse of the process of human development, from a “sensorium commune” to a being with five differentiated senses. This argument can be summarized, as Herder himself wrote, into the motto “sentio, ergo sum”, as opposed to the Cartesian “cogito, ergo sum”.

This dissertation explores the natural philosophy of the polymath Louis-Bertrand Castel (1688-1757), one of the most prolific and colorful Jesuit thinkers of early modern France. It approaches Castel’s writings as part of a coherent and insightful enterprise and shows the importance of avoiding facile categorizations of his world system as “Aristotelian,” “Cartesian” or “Anti-Newtonian” in favor of a sensitive biographical and historical contextualization of his oeuvre. Castel believed that God invested human beings with the duty and power to shape the earth, and he developed an all-embracing philosophy upon this notion. He argued that human activity occasioned rains, storms, and natural disasters; perpetuated the existence of plants and animals; caused mountains to rise and fall, rivers to flow, and fire to burn beneath the crust; in short, it ensured the circulation, the organization, and the revitalization of the world machine. Castel’s lifelong, syncretic endeavor aimed to reconcile the mechanical philosophy of his forebears with the tenets of his faith, at a time when he felt a growing number of “moderns” were eroding the dignity and free will of man.
Although scholarship has long marginalized his work, Castel’s oeuvre emerges here at the center of eighteenth-century intellectual life. By studying the development of his theories about “the action of man upon nature” in a variety of disciplinary contexts — theology, physics, political economy, geometry, meteorology, and history —  this work allows one to better understand the relationship between these disciplines and the evolution of the early modern quest for universal knowledge. This work also participates in the reassessment of the role that the Society of Jesus played in France in the development of early modern science. Castel’s intellectual endeavor helps shift one’s understanding of the scientific revolution and its aftermath, as it features Jesuits as full participants, colleagues and even precursors to better known figures of the canon. It suggests new ways of understanding how science and religion – far from being in conflict – worked together at one point to foster Enlightenment practices and ideologies.