The appeal of ghosts to the sight has already been discussed so need not be mentioned here. But the element of invisibility enters in as a new and very terrible form of supernatural manifestation in later fiction. In spite of the general visibility, some of the most horrible tales turn on the fact that the haunter is unseen. H. G. Wells's _Invisible Man_ is a human being, not a ghost; yet the story has a curdling power that few straight ghost stories possess. Maupassant's _La Horla_ is a nightmare story of an invisible being that is terrific in its effect. The victim knows that an unseen yet definite and determined something is shut in his room with him night after night, eating, drinking, reading, sitting on his chest, driving him mad. Ambrose Bierce's _The Damned Thing_ is a gruesome story of invisibility, of a something that is abroad with unearthly power of evil, whose movements can be measured by the bending of the grasses, which shuts off the light from other objects as it passes, which struggles with the dogs and with men, till it finally kills and horribly mangles the man who has been studying it, but is never seen. Another[96] has for its central figure a being that violently attacks men and is overpowered and tied only by abnormal strength, that struggles on the bed, showing its imprint on the mattress, that is imprisoned in a plaster cast to have its mold taken, that is heard breathing loudly till it dies of starvation, yet is absolutely never visible. Blackwood's Fire Elemental may be seen moving along only by the bending of the grass beneath it and by the trail it leaves behind, for though it is audible yet it is never seen. As a brave man said of it, "I am not afraid of anything that I can _see_!" so these stories of supernatural invisibility have a chilling horror more intense than that of most ghostly tales. The element of invisibility of unmistakably present spirits is shown in other stories. [96] _What Was It? A Mystery_, by Fitz-James O'Brien. One tender story of an invisible ghost is told in _In No Strange Land_,[97] of a man killed suddenly in a wreck while on his way home to the birthday dinner his wife is preparing for him. He does not know that he has been hurt; but while his dead body lies mangled under the wreckage his spirit hurries home. He swears whimsically under his breath at some interruption and thinks with joy of the happy little group he will meet. But when he enters his home he cannot make them see or hear him. They are vaguely aware of some strange influence, are awed by it, and the little son with the poet's heart whispers that he hears something, but that is all. The man stands by, impotently stretching out his arms to them till he hears the messenger tell them that he is dead. [97] By Katherine Butler.