CREATE TABLE table_26637 ("State  ( class ) " TEXT, "Vacator" TEXT, "Reason for change" TEXT, "Successor" TEXT, "Date of successors formal installation" TEXT)

What state had william bigler (d) as a successor)
SELECT "State (class)" FROM table_26637 WHERE "Successor" = 'William Bigler (D)'
SELECT "State (class)" FROM "table_26637" WHERE "Successor" = 'William Bigler (D)'