(To be continued.)
[From Household Words.]
THE PLANET-WATCHERS OF GREENWICH.
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 movable, 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 labors 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 afterward 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 gayety—once within the Observatory boundary, the first feeling is that of isolation. There is a curious stillness about the place, and the foot-step 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.
The part of the Observatory so conspicuous from without is the portion least used within. When it was designed by Christopher Wren, the general belief was that such buildings should be lofty, that the observer might be raised toward the heavenly bodies whose motions he was to watch. More modern science has taught its disciples better; and in Greenwich—which is an eminently practical Observatory—the working part of the building is found crouching behind the loftier towers. These are now occupied as subsidiary to the modern practical building. The ground floor is used as a residence by the chief astronomer; above is the large hall originally built to contain huge moveable telescopes and quadrants—such as are not now employed. Nowadays, this hall occasionally becomes a sort of scientific counting-house—irreverent but descriptive term—in which, from time to time, a band of scientific clerks are congregated to post up the books, in which the daily business of the planets has been jotted down by the astronomers who watch those marvelous bodies. Another portion is a kind of museum of astronomical curiosities. Flamstead and Halley, and their immediate successors, worked in these towers, and here still rest some of the old, rude tools with which their discoveries were completed, and their reputation, and the reputation of Greenwich, were established. As time has gone on, astronomers and opticians have invented new, and more perfect, and more luxurious instruments. Greater accuracy is thus obtainable, at a less expenditure of human patience and labor; and so the old tools are cast aside. One of them belonged to Halley, and was put up by him a hundred and thirty years ago; another is an old brazen quadrant, with which many valuable observations were made in by-gone times; and another, an old iron quadrant, still fixed in the stone pier to which it was first attached. Some of the huge telescopes that once found place in this old Observatory, have been sent away. One went to the Cape of Good Hope, and has been useful there. Another of the unsatisfactory, and now unused instruments, had a tube twenty-five feet long, whose cool and dark interior was so pleasant to the spiders that, do what they would, the astronomers could not altogether banish the persevering insects from it. Spin they would; and, spite of dusting and cleaning, and spider-killing, spin they did; and, at length, the savans got more instruments and less patience, and the spiders were left in quiet possession. This has been pleasantly spoken of as an instance of poetical justice. It is but fair that spiders should, at times, have the best of astronomers, for astronomers rob spiders for the completion of their choicest instruments. No fabric of human construction is fine enough to strain across the eyepiece of an important telescope, and opticians preserve a particular race of spiders, that their webs may be taken for that purpose. The spider lines are strained across the best instruments at Greenwich and elsewhere; and when the spinners of these beautifully fine threads disturbed the accuracy of the tube in the western wing of the old Observatory, it was said to be but fair retaliation for the robberies the industrious insects had endured.
A narrow stair leads from the unused rooms of the old Observatory to its leaded roof, whence a magnificent view is obtained; the park, the hospital, the town of Greenwich, and the windings of the Thames, and, gazing further, London itself comes grandly into the prospect. The most inveterate astronomer could scarcely fail to turn for a moment from the wonders of the heavens to admire these glories of the earth. From the leads, two turrets are reached, where the first constantly active operations in this portion of the building, are in progress.
At the present time, indeed, these turrets are the most useful portions of the old building. In one is placed the well-known contrivance for registering, hour after hour, and day after day, the force and direction of the wind. To keep such a watch by human vigilance, and to make such a register by human labor, would be a tedious, expensive, and irksome task; and human ingenuity taxed itself to make a machine for perfecting such work. The wind turns a weather-cock, and, by aid of cog-wheels the motion is transferred to a lead pencil fixed over a sheet of paper, and thus the wind is made to write down the direction which itself is blowing. Not far distant is a piece of metal, the flat side of which is ever turned by the weather-cock to meet the full force of the wind, which, blowing upon it, drives it back against a spring. To this spring is affixed a chain passing over, pullies toward another pencil, fixed above a sheet of paper, and moving faithfully, more or less, as the wind blows harder or softer. And thus the "gentle zephyr" and the fresh breeze, and the heavy gale, and, when it comes, the furious hurricane, are made to note down their character and force. The sheet of paper on which the uncertain element, the wind, is bearing witness against itself, is fixed upon a frame moved by clock-work. Steady as the progress of time, this ingenious mechanism draws the paper under the suspended pencils. Thus each minute and each hour has its written record, without human help or inspection. Once a day only, an assistant comes to put a new blank sheet in the place of that which has been covered by the moving pencils, and the latter is taken away to be bound up in a volume. The book might with truth be lettered, "The History of the Wind; written by Itself"—an Æolian autobiography.