Christopher Lyon, ed., Contemporary Art in Context, New York: The Museum of Modern Art, 1990, pp. 46–47

Duchamp is difficult to talk about because his work is so rich in its complexity. For me, it changed the way artists see their activity: we no longer believe, simply, in certain institutionalized forms of authority in art.

There is a brief to be made as an artist against certain forms, because those forms constitute fixed meanings. Readymades that are naturalized as the language of art are not seen, in fact, as ready-made. Any artist who goes to art school, who is given a canvas and paint, realizes that you didn't invent those mediums. It's given to you, and that's a Readymade. But because our conception of art acknowledges the authority of that form it's considered a naturally given one.

Institutions of art...are another framing device. One of my favorite stories...happened some years ago, when Duchamp died. They [The Museum of Modern Art] put together a small installation of some Duchamps from the collection. One was a Rotorelief: it was set on a pedastal and next to it was a text by Mr. William Rubin which discussed why this was a masterpiece of the twentieth century, declared that it smashed forever the boundaries between painting and sculpture, and went on like that in a very interesting and intelligent way. On the pedastal was a big sign that said "Please do not touch the sculpture."

In one way, this reflects a problem of any museum that serves the public, but it points to something fundamental. Basically, art is making meaning. In a sense, it's philosophy made concreted, in a period in which one can no longer believe in speculative philosophy, which has become an academic activity. Art alone answers certain questions and deals with certain issues in the world. It clarifies and makes visible how our consciousness is formed in mass culture, and takes mass culture and suese it in a way that reveals the whole internal mechanism of culture. That is a very important human role of art in a period when we don't have the spiritual satisfaction that a traditional religion can give us and the kind of cultural perks that come from homogeneous culture in which, as you get older, life is more meaningful and death is meaningful. Science as a religion deprives us of that, and so, as we continue, we are finding art is more and more valuable to people.

Anne D'Harnoncourt and Kynaston McShine, eds., Marcel Duchamp, New York: The Museum of Modern Art, 1973, p. 298

When this machine is in operation, the black eccentric circles painted on the rotating demisphere appear to undulate, producing a hypnotic illusion of space and depth.

Francis M. Naumann, The Mary and William Sisler Collection, New York: The Museum of Modern Art, 1984, pp. 204–209

The motorized construction is the culminating product in a long series of optical experiments that began with Duchamp's first concerns to seek a method of representing the fourth dimension in his work. In addition to a number of extremely varied and innovative approaches, Duchamp consistently tried to represent this higher dimensional state by means of projection—a method that was inevitably confined to the restrictions imposed by the natural two- and three-dimensional world we occupy. Around 1920 he appears to have begun a series of experiements with spinning concentric circles and spirals, geometric forms that possess an inherent ability to project an added dimension and thus were perfectly suited to Duchamp's preoccupation with the fourth dimension.

In an exceptionally long note that was recently discovered among Duchamp's papers, he describes a system of rotation whereby the spinning movement of circular shapes displaced along the pattern of a spiral will generate the illusion of depth: "The spiral at rest doesn't give any impression of relief (or at least only imagined psychologically)," he observed, but "turning around the center of one of these circles the spiral gives the impression of corkscrewing up toward the eye."(1) This principle was applied to a series of cicular disks designed to produce the effect of depth when placed in rotation, disks that were later incorporated in Duchamp's only completed film, Anemic Cinema (1925), as well as in his edition of Rotoreliefs (1935), six card-board disks especially designed to create the illusion of depth when rotated on the turntable of a record player.

Duchamp ended this long note on spirals with the words "Spheres. Hemispheres / Convexity, concavity," which might represent his earliest thoughts on the design of a three-dimensional apparatus for demonstrating perceptual illusions that occur when these geometric shapes are viewed in motion. In New York in 1920 Duchamp had already constructed an elaborate motorized device that created the sensation of compressing depth when a series of fragmented circular shapes, placed on five separate planes of glass, were properly aligned and set into a rapid spinning motion: Rotary Glass Plates (Precision Optics). And in 1925 Duchamp was provided with the opportunity to construct a second mechanical device—the Rotary Demisphere (Precision Optics)—this one designed to create the illusion of depth by the spinning motion of a geometric design. In the fashion of his earlier rotating disks, for this elaborate construction of Duchamp created a geometric design that consisted of nothing more than a series of inscribed, concentric circles, aligned tangentially to the inner configuration of a spiral motif. "I made a little thing that turned," Duchamp later explained, "that visually gave a corkscrew effect...At first I made it with spirals...not even spirals—they were off-center circles which, inscribed one inside the other, formed a spiral, but not in the geometric sense; rather in the visual effect. I was busy with that from 1921 to 1925."(2)

But rather than create the illusion of a compressed space—the visual result of the spinning Rotary Glass Plates—the rotating spiral in this second mechanical device was designed to achieve precisely the opposite effect: to create the illusion of an additional dimension. By using a geometric shape that, when spun, had already proven to generate the illusion of an added dimension and by superimposing this shape onto the surface of a three-dimensional body—as Duchamp did to the hemispherical globe of this machine—then a supplemental or higher dimensional state is consequently invoked when the whole ensemble is set into a rotary motion.

We will probably never know whether or not these complicated optical effects were explained in all their nuances and significance to the wealthy Parisian collector Jacques Doucet, who in February 1924 (probably through the instigation of his artistic advisor, André Breton) agreed to supply the necessary financial support for the design and construction of the machine.(3) Upon receipt of 6,000 francs to begin work on the project, Duchamp replied to Doucet that he considered the money "an exchange and not a payment," adding "I would like to make you a gift of this demisphere."(4) Over the course of the next seven months, Duchamp kept his financial backer continuously informed of every detail in the step-by-step construction of this machine and its components.

On March 7, 1924, he wrote a note to the collector informing him that he had purchased a base from "a dealer in apparatuses of medical electricity," and in the same message he told Doucet of an appointment he had arranged with "an 'engineer' who'll give me an estimate after he hears my requirements."(5) Just over a week later, Duchamp again wrote to Doucet, explaining how he argued with the engineer over the high price of his estimate, and how he "cut the discussion short by telling him [the engineer] in no uncertain terms that the maximum sum [he would pay] was 2,500 francs." In April he again addressed his patron, this time asking for his help in locating a suitable material for the "backing on the metal plate which supports the spiral." With follow-up reports made periodically over the course of teh next few months, by August he was ready to report "in spite of all the details the object will run by the end of September at the latest." But because of a variety of complications, the apparatus would not actually be completed until later in the year.

One of the last details to be worked out in the construction of the device pertained to the fabrication of the metial housing that was designed to support the glass globe and cover the projecting wooden hemisphere upon which the spiral was painted. On October 31, 1924, Duchamp sent another letter to his patron, supplying him with a description and sketch of this protective covering which Doucet had not yet seen: "On a copper disk," Duchamp wrote, "at the edge and all around, I had a saying engraved by an engraver—geographer—who did a remarkable job for me." Along with this note Duchamp enclosed the engraver's bill for 300 francs and declared, "Next week everything will be finished." In an earlier letter, Duchamp explained to Doucet that he found the lettering on this copper housing indespensible, "especially," as he put