It will be readily understood that with five principal telescopes in constant work and one or two minor ones, some demanding two observers, others only one, each telescope having its special programme and its special hours of work, whilst by no means every member of the staff is authorized to observe with all instruments indifferently, it becomes a somewhat intricate matter to arrange the weekly _rota_ in strict accordance with the foregoing principle, and with the further one, that whilst a considerable amount of Sunday observing is inevitable, the average duty of an observer should be three days a week, not seven days a fortnight. There is a story, received with much reserve at Cambridge, that there was once a man at that university who had mastered all the colours and combinations of shades and colours of the various colleges and clubs. If so gifted a being ever existed, he may be paralleled by the Greenwich assistant who can predict for any future epoch the sequence of duties throughout the entire establishment. At any rate, one of the first items in the week's programme is the preparation of the _rota_ for the week, or rather, to use an ecclesiastical term, for the 'octave,' _i.e._ from the Monday to the Monday following. The special work to be carried out on any telescope is likewise a matter of programme. For the transit circle a list of the most important objects to be observed is supplied for the observer's use, and the general lines upon which the other stars are to be selected from a huge 'Working Catalogue' are well understood. With some of the other telescopes the principles upon which the objects are to be selected are laid down, but the actual choice is left to the discretion of the observer at the time. There is no time for the watcher to spend in what the outsider would regard as 'discovery'; such as sweeping for comets or asteroids, hunting for variable stars, sketching planets, and so forth. Indeed, there is a story current in the Observatory that some fifty years ago, when the tide of asteroid discovery first set in, Airy found an assistant, since famous, working with a telescope on his 'off-duty' night. That stern disciplinarian asked what business the assistant had to be there on his free night, and on being told he was 'searching for new planets,' he was severely reprimanded and ordered to discontinue at once. A similar energy would not meet so gruff a discouragement to-day; but the routine work so fully occupies both staff and telescopes that an assistant may be most thoroughly devoted to his science, and yet pass a decade at the Observatory without ever seeing those 'show places' of the sky which an amateur would have run over in the first week after receiving his telescope. For example, there is no refractor in the British Isles so competent to bring out the vivid green light of the great Orion nebula--that marvellous mass of glowing, curdling, emerald cloud--or