Yesterday while riding the Q train into Manhattan, my friend Maggie and I made a joyful discovery! She noticed it first — flashes of graffiti that looked cute, almost childlike. Then as we watched, the recurring images resolved themselves into an animation, a kind of underground zoetrope.

I was too slow with the video camera to catch it, but courtesy of YouTube, you can see it above. A little googling revealed that the work is called Masstransiscope, and was installed on a disused subway platform by independent filmmaker Bill Brand in 1980. Evidently it fell into disrepair, but was restored in 2008.

The piece is pure joy. It has no other purpose than to be a surprising bright spot in a morning commute, an interjection of whimsy into the dark underground. Does that make it frivolous? It reminds me of a post I wrote last summer about public art, which speculated on the purpose and value of art commissioned for communal spaces. The post was a response to an article that disparaged recent works in this field as amusing but “relatively empty experiences,” and in it I argued that joy is a very valid, and indeed, an important purpose for public art.

Recently, I read something that bolstered my conviction on this point. In Architecture of Happiness, Alain de Botton references a theory advanced at the turn of the 20th century by German art historian Wilhelm Worringer. One component of his theory explains our collective taste in art as a kind of craving for what we lack as a society. In de Botton’s words, a society “would love in art whatever it did not possess in sufficient supply within itself. Public art, then, serves a critical rebalancing function, especially in cities. Color, light, and playful forms restore harmony to a dense gray city. Lighthearted art creates moments that break the stress of urban living. Soft sculptures create ease in a hard, concrete landscape. They are emotional oases, and in my view, they are essential to a vibrant, healthy city life.

I think there’s food for further thought here. Some things have no justification on rational grounds. They could seem pointless or even wasteful, but our increasing awareness of the importance of emotion may illuminate their value. What else seems frivolous or unnecessary, but might actually be vital because of its emotional function?