Two halves of a spiralling wooden dome face each other outside Bristol’s School of Chemistry, so the structure reads as two enormous palms pressed together. Dichroic panels colour it like stained glass and a mirrored floor hands back the sky and the weather; after dark it glows from inside. Luke Jerram hung his Extinction Bell in it, which rings at random between 150 and 200 times a day, once for every species estimated to vanish in 24 hours.