Published in 1964, “Notes on Camp” launched the career of Susan Sontag and put a spotlight, as she wrote in the essay’s first line, on “a certain mode of aestheticism.” This year’s spring exhibition at the Met Costume Institute traces the history of camp from Molière to the 20th century (with stops in the French court and 19th-century London), then flies over the rainbow with a finale of 106 high-fashion ensembles, each an embodiment of camp. —L.J.