A prayer for good grades? A hymn of praise for Princeton? A job after graduation? What tune this angelic-looking student and his fellow a cappella singers were performing is anyone’s guess. But according to archivists, their location was Blair Arch and their ­presentation took place in the 1960s. Princeton’s current a cappella groups often take advantage of Blair Arch’s acoustics, holding “arch sings” on weekend nights. Can any PAW readers identify this joyful soloist, name his performing group, or remember the occasion?