The media pavilion for the 2002 Swiss National Expo was a cloud. Organizers built a curved building fitted with more than 30,000 nozzles that pumped water from Lake Neuchâtel into a fine mist, creating a floating 90-meter fog bank whose contours were controlled by a computerized weather system.

Artist Antony Gormley took this idea a step further in 2007 with Blind Light, a 10-meter-square glass vitrine filled with mist and lit by 7,000 lux of intense fluorescent light that reduced visibility to less than an arm’s length.

“One could, and did, get temporarily lost in its 90 percent humidity,” writes Richard Hamblyn in Clouds: Nature and Culture (2017). “The intended effect of Gormley’s ‘bright, cuboid cloud’ was to overwhelm the senses, as though one had walked into a cloud, literally and figuratively, entering a cold, damp, unsettling world of enveloping isolation.”

Guillaume de Machaut’s Rondeau 14, from the 14th century, is a crab canon over a palindrome: When the singers reach the end of the line, the tenor (the lowest voice) reverses course and reads his music backward, and the other two voices follow suit, exchanging parts.

So they arrive where they started. De Machaut titled the piece “Ma fin est mon commencement” — “In my end is my beginning.”

Sculptor Giovanni Strazza probably completed this bust of a veiled Virgin Mary in the early 1850s. It was transported to Newfoundland and placed in the Episcopal Palace next to St. John’s Basilica.

“To say that this representation surpasses in perfection of art, any piece of sculpture we have ever seen, conveys but weakly our impression of its exquisite beauty,” wrote a local newspaper. “The possibility of such a triumph of the chisel had not before entered into our conception. Ordinary language must ever fail to do justice to a subject like this — to the rare artistic skill, and to the emotions it produces in the beholder.”

In 1919, engineer James Cowan Smith bequeathed £55,000 to the National Gallery of Scotland.

He set two conditions. One was that the gallery provide for his dog Fury.

The other was that this picture of his previous dog Callum, by painter John Emms, always be hung in the gallery.

Both conditions were fulfilled.

Robert Doisneau’s iconic photograph of young love in Paris sold thousands of posters, but the identity of the couple remained a mystery for decades. In 1988 Jean-Louis and Denise Lavergne saw it on a magazine cover and thought they recognized themselves: They’d been on the rue de Rivoli on April 1, 1950, and had a diary to prove it, and Lavergne still had the skirt and jacket she’d worn that day. They contacted Doisneau, who greeted them warmly but did not offer to share any of the five-figure income he’d been making each year from the poster.

When they sued him, he revealed that he’d posed the shot using Françoise Delbart and Jacques Carteaud, a couple he’d seen kissing in the street but had not dared at first to photograph. Finally he’d approached them and asked them to repeat the kiss. Delbart said, “He told us we were charming, and asked if we could kiss again for the camera. We didn’t mind. We were used to kissing.”

A thousand bubbles burst, the Lavergnes lost their suit, and Delbart eventually sold the print Doisneau had given her to feign a spontaneous kiss. She didn’t share the proceeds with Carteaud — they’d broken up nine months after the photo was taken.

What is Chopin’s B Minor Sonata? What constitutes its identity? Not the fact that it’s part of Chopin’s conscious experience, because it continues to exist after his death. And not the fact that it’s part of any listener’s experience, because it continues to exist when those experiences have ended. It can’t be identified with any particular performance, and it’s different from its score, since the sonata is a sounding work and the score is an arrangement of graphic signs.

If the sonata is not material, and if it’s different from the experience of both the composer and the listener (in fact, it continues to exist if no one takes any conscious interest in it at all), how can it exist? How do we discern the same “original” work in a hundred different performances?

Is the sonata an ideal object, immutable and atemporal, like a mathematical concept? Well, no, because Chopin created it at a particular time. Perhaps there is no sonata, only individual performances? But then there’d be no sense in distinguishing a performance from the work itself, or in talking about the identity of a work (“Chopin’s B Minor Sonata”), or in arguing over whether a given performance was faithful to the original.

“For what is the point of saying that one performance rather than another gives a more nearly accurate account of the B Minor Sonata when the sonata does not in fact exist and when there is nothing real with which these performances may be compared?” asks philosopher Roman Ingarden. “Are we really going to agree that such judgments concerning the sonata itself and its performances are all false and stupid?”

(Roman Ingarden, The Work of Music and the Problem of Its Identity, 1986.)

Matthieu Robert-Ortis makes cleverly ambiguous wire sculptures.

More at his website.