CREATE TABLE table_18739 ("District" TEXT, "Incumbent" TEXT, "Party" TEXT, "First elected" FLOAT, "Result" TEXT, "Candidates" TEXT)

Which District was the incumbent Julius Kahn from? Answer: California 4th district
SELECT COUNT("District") FROM table_18739 WHERE "Incumbent" = 'Julius Kahn'
SELECT COUNT("District") FROM "table_18739" WHERE "Incumbent" = 'Julius Kahn'