Close by is another contrivance for registering in decimals of an inch the quantity of rain that falls. The drops are caught, and passing down a tube, a permanent mark is made by which the quantity is determined.
The eastern turret is devoted to the Time Ball and its mechanism. Far out at sea—away from all sources of information but those to be asked of the planets, his compass, his quadrant, his chronometer, and his almanack, the mariner feels the value of time in a way which the landsman can scarcely conceive. If his chronometer is right, he may feel safe; let him have reason to doubt its accuracy, and he knows how the perils surrounding him are increased. An error of a few seconds in his time may place him in danger—an error of a few minutes may lead him to steer blindly to his certain wreck. Hence his desire when he is leaving port to have his time-pieces right to a second; and hence the expenditure of thought, and labor, and money, at the Greenwich Observatory, to afford the shipping of the great port of London, and the English navy, the exact time—true to the tenth of a second, or six hundredth of a minute—and to afford them also a book, the Nautical Almanack, containing a mass of astronomical facts, on which they may base their calculations, with full reliance as to their accuracy. Every day for the last seventeen years, at five minutes before one o'clock, the black ball five feet across and stuffed with cork, is raised halfway up its shaft above the eastern turret of the observatory—at two-and-a-half minutes before that hour, it rises to the top. Telescopes from many a point, both up and down the river, are now pointed to this dark spot above the Greenwich trees, and many an anxious mariner has his time-pieces beside him, that their indications may be made true. Watch the ball as you stand in the Park. It is now just raised. You must wait two minutes and a half, and as you do so, you feel what a minute may be. It seems a long, palpable, appreciable time, indeed. In the turret below, stands a clock telling the true time, gained by a laborious watching of the clock-stars; and beside the clock, is a man with a practiced hand upon a trigger, and a practiced eye upon the face of the dial. One minute—two minutes pass. Thirty seconds more, and the trigger has released the Ball. As it leaves the top of the shaft, it is one o'clock to the tenth of a second By the time it has reached the bottom it is some five seconds later.
Leaving the Ball Turret, and the old building which it surmounts, the new Observatory, where the chief work of the establishment is done, claims our notice. This attention would scarcely be given to its outward appearance for it is a long, low building, scarcely seen beyond its own boundaries. The Greenwich Observatory is not a show place, but an eminently practical establishment. St. Petersburg and other cities have much more gorgeous buildings devoted to astronomical purposes, and Russia and other countries spend much more money on astronomy than England does, yet the Greenwich Tables have a world-wide reputation, and some of them are used as the groundwork for calculations in all Observatories at home and abroad. The astronomer does not want marble halls or grand saloons for his work. Galileo used a bell-tower at Venice, and Kepler stood on the bridge at Prague to watch the stars. The men, not the buildings, do the work. No disappointment, need be felt, then, to find the modern Observatory a range of unadorned buildings running east and west, with slits in the roof and in some of the walls. Within these simple buildings are the instruments now used, displaying almost the perfection of mechanical skill in their construction and finish—beautifully adapted to the object they have to fulfill, and in perfect order. They are fixed on solid piers of masonry, deeply imbedded in the earth, to secure freedom from vibration—a quality better obtained when the foundations are on sand or gravel than when on rock.
To describe the instruments by their technical names, and to go into any particulars of the instruments they have superseded, would take space, only to do the work of a scientific treatise. Enough, therefore, to say, that there are the telescopes best adapted to the chief duty of the place, which is, watching the moon whenever she is visible; watching the clock-stars, by which the true time is calculated more exactly than it could be from observations of the sun alone; and watching other planetary bodies as they pass the meridian. Eclipses, occultations, and other phenomena, of course, have their share of attention, and add to the burden of the observer's duties.
The staff of the Observatory includes a chief astronomer, Mr. Airy, with a salary of £800 a year; and six assistants who are paid, £470, £290, £240, £150, £130, and £130, respectively. This does not include the officers of the Meteorological branch of the establishment, to be spoken of hereafter; and which consists of Mr. Glaisher, with £240 a year, one assistant at £120, and two additional computers. At times, when these scientific laborers have collected more observations than they are able to work out; additional help is summoned, in shape of the body of scientific clerks before spoken of; who, seated at desks, cast up the accounts the planetary bodies, including such regular old friends as the moon and fixed stars, but not forgetting those wandering celestial existences that rush, from time to time, over the meridian, and may be fairly called the chance customers of the astronomer.
Though the interior of the Observatory seems so still, the life of those employed there has its excitements. Looking through telescopes forms a small part only of their duty—and that duty can not be done when the weather is unfavorable. On cloudy days the observer is idle; in bright weather he is busy; and a long continuance of clear days and nights gives him more employment than he can well complete. Summer, therefore, is his time of labor; winter his time of rest. It appears that in our climate the nights, on the whole, are clearer than the days, and evenings less cloudy than mornings. Every assistant takes his turn as an observer, and a chain of duty is kept up night and day; at other periods, the busiest portion of the twenty-four hours at the Observatory, is between nine in the morning and two in the afternoon. During this time they work in silence, the task being to complete the records of the observations made, by filling in the requisite columns of figures upon printed forms, and then adding and subtracting them as the case requires. While thus engaged, the assistant who has charge of an instrument looks, from time to time, at his star regulated clock, and when it warns him that his expected planet is nearly due, he leaves his companions, and quietly repairs to the room where the telescope is ready. The adjustment of this has previously been arranged with the greatest nicety. The shutter is moved from the slit in the roof, the astronomer sits upon an easy chair with a movable back. If the object he seeks is high in the heavens, this chair-back is lowered till its occupant almost lies down; if the star is lower, the chair-back is raised in proportion. He has his note-book and metallic pencil in hand. Across the eye-piece of the telescope are stretched seven lines of spider-web, dividing the field of view. If his seat requires change, the least motion arranges it to his satisfaction, for it rests upon a railway of its own. Beside him is one of the star-clocks, and as the moment approaches for the appearance of the planet, the excitement of the moment increases. "The tremble of impatience for the entrance of the star on the field of view," says an Edinburgh Reviewer, "is like that of a sportsman whose dog has just made a full point, and who awaits the rising of the game. When a star appears, the observer, in technical language, takes a second from the clock face; that is, he reads the second with his eye, and counts on by the ear the succeeding beats of the clock, naming the seconds mentally. As the star passes each wire of the transit, he marks down in his jotting-book with a metallic pencil the second, and the second only, of his observation, with such a fraction of a second as corresponds, in his judgment, to the interval of time between the passage of the star, and the beat of the clock which preceded such passage."
An experienced observer will never commit an error in this mental calculation, exceeding the tenth of a second, or six hundredth of a minute. When the star has been thus watched over the seven cobweb lines (or wires), the observer jots down the hour and minute, in addition to the second, and the task is done. Stars, not very near the sun, may be seen in broad daylight, but, at night, it is requisite to direct a ray of light from a lamp, so far to enlighten the field of the telescope, as to permit the spider lines to be seen running across the brighter ground on which the expected star is to be visible.
The adjustment of the instruments is a task of great nicety. If they are out of trim only a shadow of a shade of a hair's-breadth, the desired accuracy is interfered with, and they have to be re-adjusted. Temperature is of course an important element in their condition, and a slight sensibility may do mischief. The warmth of the observer's body, when approaching the instruments, has been known to affect their accuracy; and to avoid such sources of error, instruments have at times been cased in flannel, that the non-conducting powers of that homely fabric might screen the too-sensitive metal.
Sunday is a comparative holiday at the Observatory, for then, except when any extraordinary phenomena are expected, the only duty done is to drop the Time Ball, and observe the moon's place. The moon is never neglected, and her motions have been here watched, during the last hundred and seventy years, with the most pertinacious care—to the great service of astronomy, and the great benefit of navigation.
The library should not pass unnoticed. It is small; but being devoted to works upon astronomy, and the kindred sciences, there is ample room for all that has hitherto been written on the subject, or that can, for many generations, be produced. The observations of a lifetime spent in watching the stars may be printed in marvelously few pages. A glance through the Greenwich Astronomical Library gives a rough general idea of what the world has done and is doing for the promotion of this science. Russia contributes large, imperial-looking tomes, that tell of extended observations made under the munificent patronage of a despot; Germany sends from different points a variety of smaller, cheaper-looking, yet valuable contributions; France gives proofs of her genius and her discoveries; but her forte is not in observation. The French are bad observers. They have no such proofs of unremitting, patient toil in search of facts, as those afforded in the records of the Greenwich Tables of the Moon. Indeed, Greenwich, as we have already said, is a working Observatory; and those who go into its library, and its fire-proof manuscript-room, and see how its volumes of observations have been growing from the small beginnings of the days of Flamstead and Halley, to those of our later and more, liberal times, will have good reason to acknowledge that the money devoted to this establishment has been well employed.