The Royal Observatory, Greenwich: A Glance at Its History and Work

by E. Walter Maunder

But of late years another method has proved available. Distant nations are now woven together across thousands of miles of ocean by the submarine telegraph. The American reads in his morning paper a summary of the debates of the previous night in the House of Commons at Westminster. The Londoner watches with interest the scores of the English cricket team in Australia. It is now therefore possible for an astronomer in England to record, should he so desire, the time of the transit of a star across the wires of his instrument, not only on his own chronograph, but upon that of another observatory, it may be 2000 miles away. Or, much more conveniently, each observer may independently determine the error of his own clock, and then bring his clock into the current, so that it may send a signal to the chronograph of the other station.

In one way or another this work of the determination of geographical longitudes has been an important part of the extra-routine work at Greenwich, part of the work which has built up and sustained its claim to define 'longitude nought'; and many distinguished astronomers, especially from the leading observatories of the Continent, have come here from time to time to obtain more accurately the longitude of their own cities. The traces of their visits may be seen here and there about the Observatory grounds in flat stones which lie level with the surface, and bear a name and date like the gravestones in some old country churchyard. These are not, as one might suppose, to mark the burial-places of deceased astronomers, but record the sites where, on their visits for longitude purposes, different foreign astronomers have set up their transit instruments. Now, however, a permanent pier has been erected in the courtyard, and a neat house—the Transit Pavilion—built over it, so that in all probability no fresh additions will be made to these sepulchral-looking little monuments.

It might be asked, What reason is there for a foreign observer to come over to England for such a purpose? Would it not be sufficient for the clock signals to be exchanged? But a curious little fact has come out with the increase of accuracy of transit observation, and that is, that each observer has his own particular habit or method of observation. A hundred years ago, Maskelyne, the fifth Astronomer Royal, was greatly disturbed to find that his assistant, David Kinnebrook, constantly and regularly observed a star-transit a little later than he did himself. The offender was scolded, warned, exhorted, and finally, when all proved useless to bring his observations into exact agreement with the Astronomer Royal's, dismissed as an incompetent observer. As a matter of fact, poor Kinnebrook has a right to be regarded as one of the martyrs of science, and Maskelyne, by this most natural but mistaken judgment, missed the chance of making an important discovery, which was not made until some thirty years later. Astronomers now would be more cautious of concluding that observations were bad simply because they differed from what had been expected. They have learnt by experience that these unexpected differences are the most likely hunting-ground in which to look for new discoveries.

In a modern transit observation with the use of the chronograph it will be seen at once that before the observer can register a star-transit on the chronograph, he has to perceive with his eye that the star has reached the wire, he has to mentally recognize the fact, and consciously or unconsciously to exert the effort of will necessary to bring his finger down on the button. A very slight knowledge of character will show that this will require different periods of time for different people. It will be but a fraction of a second in any case, but there will be a distinct difference, a constant difference, between the eager, quick, impulsive man who habitually anticipates, as it were, the instant when he sees star and wire together, and the phlegmatic, slow-and-sure man who carefully waits till he is quite sure that the contact has taken place, and then deliberately and firmly records it. These differences are so truly personal to the observer that it is quite possible to correct for them, and after a given observer's habit has become known, to reduce his transit times to those of some standard observer. It must, of course, be remembered that this 'personal equation' is an exceedingly minute quantity, and in most cases is rather a question of hundredths of seconds than of tenths.

It will be seen from the foregoing description how little of what may be termed the picturesque or sensational side of astronomy enters into the routine of the Time Department, the most important of all the departments of the Observatory. The daily observation of sun and of many stars—selected from a carefully chosen list of some hundreds, and known as 'clock stars'—the determination of the error of the standard clock to the hundredth of a second if possible, and its correction twice a day, the sending out of time signals to the General Post Office and other places, whence they are distributed all over the country; the care, winding, and rating of hundreds of chronometers and chronometer watches, and from time to time the determination of the longitude of foreign or colonial cities, make up a heavy, ceaseless routine in which there is little opportunity for the realization of an astronomer's life as it is apt to be popularly conceived.

Yet there is interest enough in the work. There is the charm which always attaches to work of precision, the delight of using delicate and exact instruments, and of obtaining results of steadily increasing perfection. It may be akin to the sporting passion for record-breaking, but surely it is a noble form of it which has led the assistants, in recent years, to steadily increase the number of observations in a normal night's work up to the very limit, taking care the while that their accuracy has in no degree suffered. In longitude work also 'the better is the enemy of the good,' and there is the ambition that each fresh determination shall be markedly more precise than all that have preceded it. The constant care of chronometers soon reveals a kind of individuality in them which forms a fresh source of interest, whilst if a man has but a spark of imagination, how easily he will wrap them round with a halo of romance!

Glance through the ledgers, and you will see how some of them have heard the guns at the siege of Alexandria, others have been carried far into the frozen north, others have wandered with Livingstone or Cameron in the trackless forests of equatorial Africa.

More striking still are those pages across which the closing line has been drawn; never again will the time-keeper there scheduled return to the kindly inquisition of Flamsteed Hill. This sailed away in the Wasp, and was swallowed up in the eastern typhoon; that went down in the sudden squall that smote the Eurydice off the Isle of Wight; these foundered with the Captain. The last fatal journey of Sir John Franklin to find the North-West Passage leaves its record here; the chronometers of the Erebus and Terror will never again appear on the Greenwich muster roll. Land exploration claims its victims too. Sturt's ill-fated expedition across Australia, and Livingstone's last wandering, are represented.