CREATE TABLE table_79848 ("Rider" CLOB, "Date" CLOB, "Place" CLOB, "Race" CLOB, "Event" CLOB, "Machine" CLOB)

Harry l Stephen rides a Norton machine on what date?
SELECT "Date" FROM table_79848 WHERE "Machine" = 'norton' AND "Rider" = 'harry l stephen'
SELECT "Date" FROM "table_79848" WHERE "Machine" = 'norton' AND "Rider" = 'harry l stephen'