CREATE TABLE table_52908 ("Ship" TEXT, "Date Commissioned" FLOAT, "Gross Tonnage" FLOAT, "Propulsion" TEXT, "Material" TEXT)

Tell me the sum of Gross Tonnage for isis ship on date commisioned less than 1842
SELECT SUM("Gross Tonnage") FROM table_52908 WHERE "Ship" = 'isis' AND "Date Commissioned" < '1842'
SELECT SUM("Gross Tonnage") FROM "table_52908" WHERE "Date Commissioned" < '1842' AND "Ship" = 'isis'