The spatial and conceptual center of Sam Porritt’s show “A Certain Change” is a slender, five-foot-nine-inch-tall wood-and-plaster sculpture that resembles the nineteenth-century Eddystone Lighthouse on the Cornish coast. This motorized artwork, titled Lost at Sea (all works 2018), continually rotates about its own axis, and its beam radiates out into the city: Living up to its name, Vitrine is an entirely transparent glass pavilion. Set around a bridge pier, the gallery and a companion structure that houses a fast-food stand were built as part of the redesign of a former railway-station square