There is a morsel of Greenwich Park, which has, for now nearly two centuries, been held sacred from intrusion. It is the portion inclosed by the walls of the Observatory. Certainly a hundred thousand visitors must ramble over the surrounding lawns, and look with curious eye upon the towers and outer boundaries of that little citadel of science, for one who finds admission to the interior of the building. Its brick towers, with flanking turrets and picturesque roofs, perched on the side of the gravelly hill, and sheltered round about by groups of fine old trees, are as well known as Greenwich Hospital itself. But what work goes on inside its carefully preserved boundary and under those moveable, black-domed roofs, is a popular mystery. Many a holiday-maker’s wonder has been excited by the fall, at one o’clock, of the huge black ball, high up there, by the weather vane on the topmost point of the eastern turret. He knows, or is told if he asks a loitering pensioner, that the descent of the ball tells the time as truly as the sun; and that all the ships in the river watch it to set their chronometers by, before they sail; and that all the railway clocks, and all the railway trains over the kingdom are arranged punctually by its indications. But how the heavens are watched to secure this punctual definition of the flight of time, and what other curious labours are going on inside the Observatory, is a sealed book. The public have always been, of necessity, excluded from the Observatory walls, for the place is devoted to the prosecution of a science whose operations are inconsistent with the bustle, the interruptions, the talk, and the anxieties of popular curiosity and examination. But when public information and instruction are the objects, the doors are widely opened, and the press and its _attachés_ find a way into this, as into many other sacred and forbidden spots. Only last week one of ‘our own contributors’ was seen in a carriage on the Greenwich railway, poring over the paper in the last Edinburgh Review that describes our national astronomical establishment, and was known afterwards to have climbed the Observatory hill, and to have rung and gained admission at the little black mysterious gate in the Observatory wall. Let us see what is told in his report of what he saw within that sacred portal. In the park on a fine day all seems life and gaiety—once within the Observatory boundary, the first feeling is that of isolation. There is a curious stillness about the place, and the footsteps of the old pensioner, who closes the gate upon a visitor, echoes again on the pavement as he goes away to wake up from his astronomical or meteorological trance one of the officers of this sanctum. Soon, under the guidance of the good genius so invoked, the secrets of the place begin to reveal themselves.