Dawn 'til dusk.

"The eye is the first circle; the horizon which it forms is the second; and throughout nature this primary figure is repeated without end. It is the highest emblem in the cipher of the world." So Emerson writes in his 1841 essay "Circles." A visual corollary for this theory might be found today in the work of Olafur Eliasson, an enthusiastic examiner of horizons, orbs, and spheres of vision. Case in point: Your black horizon, 2005, the artist's latest project, housed in a temporary pavilion designed by British architect David Adjaye on the island of San Lazzaro as part of "Always a Little Further," curated by Rosa Martinez.

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When first entering this elegant wooden structure, you ascend a ramp into a darkened area that is suddenly pierced by a sharp light. Soon your pupils adjust, and you see that the light is emanating from a thin horizontal recess traversing, at eye level, the length of each wall in the room. You can follow this line while walking along the walls. Or you can position yourself at the very center of the space and turn around slowly to take in the effect of a surrounding gleaming horizon--one that could easily be miles away, since it is nearly impossible to judge distance in this place. After recovering from an initial sense of disorientation, you attend to subtle shifts in the quality of the light: Warm, reddish shades very gradually lighten into chilly, blue-tinged hues of white.

In fact, this artificial horizon reproduces the effects of the sun in transit above the Venetian Mediterranean, but a condensed version: Within fifteen minutes, every viewer can experience the rich range of color and varying degrees of brightness of light on a single day, from sunrise to sunset. (The lights have been calibrated to recordings recently made in the local setting.) As you concentrate on the luminous line, however, strange physiological effects are triggered in your eyes, and a second line, a kind of visual echo of the first, starts to travel upwards before fading away. Then a new one appears and starts to wander. The color of this drifting afterimage is hard to determine--but perhaps it really is black, as the title of the work suggests. Certainly it is "your" horizon, in the sense that it begins somewhere inside you, behind your eyes rather than in front of them, as James Turrell would insist.

This disruption in your powers of perception--complicating where the "you" begins and ends--is the current underlying much of Eliasson's work, which not only draws on artistic practices developed in the '60s and '70s by such artists as Turrell and Robert Irwin, but also on recent innovations in cognitive science and technologies for measuring and reproducing the color and strength of light. Yet with this work, it is perhaps finally clear (and more intriguing) that Eliasson iterates a solar fascination, as evinced in the artificial rainbow of Beauty, 1993; Your sun machine, 1997; and a succession of synthetic suns that culminated in the Weather Project, 2003, at Tate Modem. This heliocentric drive seems to originate in ancient speculations concerning vision and the power of the mind. Writing about the sun as the foundation of all philosophical metaphorics in "White Mythology," Jacques Derrida spelled out the limits of what is natural in nature: "Each time that there is a metaphor, there is doubtless a sun somewhere; but each time that there is sun, metaphor has begun. If the sun is metaphorical always, already it is no longer completely natural. It is always, already a luster, a chandelier, one might say an artificial construction, if one could still give credence to this signification when nature has disappeared. For if the sun is no longer completely natural, what in nature does remain natural?" That, I think, is what Eliasson, today's chief manufacturer of suns, would really like to know. Although his sun is black, the piece is this Biennale's zenith, metaphorically speaking. To dream of an art (and an experience) without metaphors, he leaves to others.

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Daniel Birnbaum is a contributing editor of Artforum.