Who was the successor for the new seat?
CREATE TABLE "table1_2147588_3" (
  "state_class" text,
  "vacator" text,
  "reason_for_change" text,
  "successor" text,
  "date_of_successors_formal_installation" text
);
SELECT "successor" FROM "table1_2147588_3" WHERE "vacator"='New seat';