I guess the house was very big and high and there should be a big skylight in the roof of it so that when the narrator came into the house, he/she was amazed by the splendid scene: sunlight could reach inside the house; and it was not veryeasy to make out the uppermost parts of the house, bedause of its highness, although it was bright in the interior; and there you could see through the skylight a far greater space in the sky than the house alone so that you felt it open and clear. All the description is to show the bigness, highness, splendidness and comfort of the house. ---- I have never seen the house, especially the probable skylight, nor have I read the orgingal, but I think here I'd be a Holmes and am right ;) :D)