“Presented with a Universal blanc”: The Physics of Vision in Milton’s Invocation to Light

But cloud instead, and ever-during darkSurrounds me, from the cheerful ways of menCut off, and for the Book of knowledge fairPresented with a Universal blancOf Nature’s works to me expung’d and ras’d,And wisdom at one entrance quite shut out.So much the rather thou Celestial LightShine inward, and the mind through all her powersIrradiate, there plant eyes, all mist from thencePurge and disperse, that I may see and tellOf things invisible to mortal sight.

Paradise Lost 3.45–55

Trapped within the darkened chamber of his blind body, the narrator of Milton’s Paradise Lost signals his ascension from the darkness of hell to the inexpressible light of heaven with an invocation that reflects upon the relationship between physical and spiritual vision. “Cut off” from the physical, visual experience of nature’s “Book of knowledge fair,” the narrator appeals to celestial light to grant him in its stead visual access to things normally “invisible to mortal sight,” that is, to the “ways of God” that he seeks to “justify” to his readers.¹ Personal in tone, the invocation is all the more powerful due to Milton’s own blindness. Yet in spite of the narrator’s extensive description of the physical experience of blindness—from his desperation as his eyes “roll in vain / To find [light’s] piercing ray” (PL 3.23–24) to his plea to light to “purge and disperse” the “dim suffusion” that has “quencht thir Orbs” (3.54, 25–26)—the invocation has rarely been discussed in terms of Milton’s understanding of the physics of vision. Instead, critical analysis has gravitated toward discussion of the Neoplatonic contexts and sources for the analogy that Milton draws between bodily sight and spiritual insight.²

In this essay I offer a different lens through which we might read Milton’s exploration of vision and blindness, one that locates his description in the context of seventeenth century models of the eye. Certainly, the invocation does turn on a comparison between physical sight and spiritual understanding that resonates with Neoplatonic thought. However, in emphasizing vision’s metaphorical register, scholars have overlooked the relevance of significant developments in seventeenth century optical science. Milton’s eye is not the eye of his classical and medieval predecessors. Over the course of the seventeenth century, the extramissive, species-based model of vision that is assumed by his Neoplatonic sources gave way to a modern model—first introduced by Johannes Kepler and further developed by René Descartes and others—that conceived of the eye as a mechanical object penetrated by light, the passive recipient of projected images. It is this passive model of vision that Milton has in mind when he describes the physical experience of being helplessly “cut off” from light and thus from the ability visually to experience Nature’s works. Perhaps even more significantly, it is this model that undergirds Milton’s figuration of the mind’s vision of divine things as a luminous piercing of the dark body—the “ir” prefix on “irradiate” stressing the inward movement—by celestial light.

In the following, I contextualize Milton’s invocation to light within the framework of the optical theory of his period by examining the parallels—and the distinctions—between the role played by light in Milton’s model of vision and the models proposed by Kepler and Descartes. I will argue that in the invocation Milton adopts not only Kepler’s theory of the retinal image but also the analogy that both Kepler and Descartes draw between the eye and a camera obscura or dark room into which light is refracted through a lens placed at a hole in one side, projecting an inverted image of exterior objects onto the opposite wall. For Kepler, this analogy serves to explain observational errors that result from the process of refraction not only in optical instruments but also in the eye itself. For Descartes, it serves to support his philosophical position that visual perception occurs in the mind, not...