Optics and the Illusion of Empiricism in the Encyclopédie

The Encyclopédie's articles in optics and vision are surprising to a modern reader who expects to find there the Newtonianism of mid-Enlightenment France or who thinks of the philosophes as conventionally empirical. Rather than accepting Newton's theories wholesale, however, the encyclopédistes put them into question over and over and at first glance seem to be attempting to recuperate a Cartesian position on the nature of light and the way the eye sees it, especially with respect to color. Let us consider one reason why this may have been the case while we nonetheless argue that this is not exactly what they were doing. To begin, though, we will need an overview of Newton's project to elucidate what otherwise might be hidden agendas.

First, we must remember that Newton was a firm, not to say fanatical believer in the Christian God. Indeed, for him the discovery of the laws of celestial mechanics as he laid them out in the Philosophiae Naturalis Principia Mathematica were a demonstration of the manifestation of the power and of the very nature of God as a god.¹ When criticized as a promoter of atheism, he answered consistently that the laws of celestial motion were not enough in themselves to cause the solar system to form and to move in the way that it does. That natural laws are descriptions of the behavior of the mechanical world and nothing else, and Newton repeated over and over that even gravity is the name of a perceived regularity, not the positing of the existence of a cause. Yet this notoriously discreet, even secretive thinker found himself obliged to deal with this issue explicitly after many an accusation that his mathematization of the heavens made materialist atheism a coherent and tenable position. In the famous General Scholium (appended to the second edition of the Principia), Newton defined God not merely as the Creator, but essentially, and fundamentally, as the Lawgiver.

This most beautiful system of the sun, planets, and comets, could only proceed from the counsel and dominion of an intelligent and powerful Being. And if the fixed stars are the centres of other like systems, these, being formed by the like wise counsel, must be all subject to the dominion of One. . . . This Being governs all things, not as the soul of the world, but as Lord over all; and on account of his dominion he is wont to be called Lord God pantokrátwr, or "Universal Ruler"; for God is a relative word, and has a respect to servants; and Deity is the dominion of God not over his own body, as those imagine who fancy God to be the soul of the world, but over servants. . . . a god without dominion, providence, and final causes, is nothing else but Fate and Nature. Blind metaphysical necessity, which is certainly the same always and everywhere, could produce no variety of things. . . .²

To cut to the chase: for Newton, to observe the regularities of the heavens is thus to peer into the lawgiving nature of God. It is not to prove that the universe is a clockwork that doesn't need a divine principle in order to either exist or function. It is essential to understand that for Newton, Law first and foremost implies the lawgiver and the verifiable status of the observations that permit the deduction of the existence of these laws then becomes a separate and corollary issue.

Now, these observations take place through vision of one sort or another, whether of the unaided eye or through the reflecting telescope that Newton perfected. In other words, they are empirically produced as we understand the word—observation through sense-based perception. But empiricism itself poses a problem. At the time, an empiric was "2. An untrained practitioner in physic or surgery; a quack. b. transf. A pretender, impostor, charlatan" (Oxford English Dictionary). From the OED, again: "Empiricism" is "The method or practice of an empiric." For our purposes, beyond the negative connotations, the no longer held but essential definition of an empiric was...