CREATE TABLE table_18953 ("Ep. No." FLOAT, "Title" CLOB, "Director" CLOB, "Written by" CLOB, "Original Air Date" CLOB, "Production No." FLOAT)

Who wrote the episode called 'mercury falling'?
SELECT "Written by" FROM table_18953 WHERE "Title" = 'Mercury Falling'
SELECT "Written by" FROM "table_18953" WHERE "Title" = 'Mercury Falling'