How many reasons for change were listed when Edward Hempstead was the successor?
CREATE TABLE "table1_225095_4" (
  "district" text,
  "vacator" text,
  "reason_for_change" text,
  "successor" text,
  "date_successor_seated" text
);
SELECT COUNT("reason_for_change") FROM "table1_225095_4" WHERE "successor"='Edward Hempstead';