midnight
`` The ghost that is common to Scotch castles and English manor-houses , and that appears in an orthodox night-gown , sighs , screams , rattles chains and bangs doors ad libitum . No , no ! That kind of ghost is composed of indigestion , aided by rats and a gust of wind . No ; when I say ghosts , I mean ghosts -- ghosts that do not need the midnight hour to evolve themselves into being , and that by no means vanish at cock-crow . My ghosts are those that move about among us in social intercourse for days , months -- sometimes years -- according to their several missions ; ghosts that talk to us , imitate our customs and ways , shake hands with us , laugh and dance with us , and altogether comport themselves like human beings . Those are my kind of ghosts -- ` scientific ' ghosts . There are hundreds , aye , perhaps thousands of them in the world at this very moment . ''