“Having consulted his list, and adjusted his telescope, he commences his steady gaze. His intentness can only be compared to that of a sportsman, or still better to that of a pointer dog, only, instead of a partridge or a woodcock, he is eagerly waiting to see a star get up. There it is at last! It comes into view quick and sudden as a meteor. Scarcely has it entered into the telegraphic field of sight than it appears to approach rapidly some objects which look like a series of transverse iron bars placed at equal distances from each other. These, however, in reality, are nothing but threads of the thickness of a spider’s web, stretched according to a system in the interior of the telescope, and wonderfully magnified by the power of the lenses.
“The assistants are all astronomers by profession, and their eyes have been well trained by continual practice. How, then, can it happen, that their observations do not always prove accordant one with another? There is a physiological mystery hidden in the fact which it would be interesting to penetrate. Each observer, although operating with the same instrument and guided by the same plan, perceives a celestial phenomenon—as, for instance, the transit of a star—either sooner or later than another does. This variation is attributed to the idiosyncrasy of the sense of sight in each individual, or to the more or less prompt manner in which the eye telegraphs its impression to the brain. It must, of course, be quite understood that no considerable inequalities of time are in question here; it is, at the most, some fraction of a second that I am alluding to; but the astronomical transit observations are of so delicate a nature, that the slightest errors would destroy their worth. Under these circumstances it has been found necessary to establish an average or standard, and each observer gets to know [pg 281]precisely how far his visual faculties vary from the ideal. Hence arises a question, incomprehensible to the uninitiated, which, however, is commonly asked among astronomers themselves—‘What is the value of your personal equation?’ This inquiry is answered by a figure expressing the particular amount of deviation from the standard. The most singular thing is, that the value of the personal equation is different in the same individual as regards the various celestial bodies. Some can very quickly discern the phenomena of a fixed star who are much slower in perceiving those of the moon, and vice versâ. In order to obviate the inconvenience which might result from the variations in personal equations, they also have recourse to a very ingenious plan. An eye-piece with two tubes allows two assistants simultaneously to observe the passage of the same star over the same threads in the instrument; [pg 282]they both listen to the ticking of the clock marking the seconds, and separately calculate the results of their observations, which are afterwards compared. To obtain a greater degree of certitude, they occasionally exchange places. In this way the slightest chances of error are eliminated. The aberrations of the instrument must also be taken into account. Notwithstanding its excellence and the solidity with which it is fixed to stone walls sunk into the ground, it sometimes is affected by slight vibrations, which can only be attributed to the terra firma on which it is constructed. Mr. Airy has noticed this same phenomenon at Cambridge, whence he has come to the conclusion ‘that the surface of the earth, commonly regarded as the base of all solidity, is itself in movement.’
THE GREAT EQUATORIAL TELESCOPE IN THE DOME, GREENWICH OBSERVATORY.
“ ‘I am going to show you the clock which sets the time for all England,’ said the Astronomer Royal to me, as he conducted me into a little room occupying one of the oldest parts of the edifice. Covered with its simple mahogany case, this Mother clock, as it is called, is not unlike one of those venerable wooden-cased clocks that one meets with sometimes in the old English manor-houses. No one, however, could fail to discover that the mechanism in this time-keeper is new and uncommon. Its chief characteristic is that it possesses two distinct attributes. In the first place it marks the time most exactly; and, in the next, it communicates this power to other clocks as well. It has therefore been called the Mother clock, because it animates in the Observatory eight of its daughters. Its dial is divided into three circles, one of which marks the hours, another the minutes, and a third the seconds. One hand only moves round each of these dials, and thus points out the generally-accepted measures of time.
“The Observatory transmits signals every hour to the telegraph-office in Lothbury, in the City of London, whence, by a network of galvanic wires, the knowledge of the true time is spread along the lines of railway to the extremities of Great Britain. This vast Æolian harp covers thus with its chords nearly the whole surface of the British Isles, and vibrates in unison with one prime mover.
“As regards the true time, these telegraphic wires have a double mission. The current leaving Greenwich transmits the signal given by the clock at the Observatory, and what is called a return current then communicates the errors of the other clock on which the Mother has just acted. ‘I would never undertake to regulate a clock from which I did not get regular replies,’ said the Astronomer Royal; and just as we were passing in front of a galvanic apparatus, ‘Stop!’ he added, ‘the great clock at Westminster is at this very moment giving me an account of itself; it goes well, and is only the twentieth part of a second slow. Twice a day in this way it keeps me informed of the state of its health.’ ”
Below Greenwich one of the saddest catastrophes of the century occurred in 1879, one which has its lessons for all who voyage. We refer to the loss of the Princess Alice. A pleasure steamer, one of the largest and best known of the London Steam-packet Company, with some 700 happy merrymakers, a large proportion of whom were children, left London Bridge on Tuesday morning, September 3rd, 1878, for Gravesend and Sheerness, and everything, even the temper of our uncertain climate, [pg 283]combined to make the day one of real and innocent pleasure. How true is it that danger is never so near as when we deem it farthest off. It was eight o’clock in the evening when the Princess Alice hove in sight off Woolwich Arsenal, with her living freight of gladsome excursionists. The song that comes when toil ceases, the careless laugh and harmless jest were going round; eager eyes watched the dim lights of home glinting through the purple September twilight, and no whispered thought of peril dulled the harmony of the day, when a large steam collier, the Bywell Castle, loomed darkly in the gloom.
Those who feared the least and knew the most from experience were the first to see the danger—the danger that, in the time, no human skill or ingenuity could avert. The Princess Alice, steaming on at good speed, had attained an impetus, and, together with the adverse tide and confined space, defeated the ready efforts of the commanders of both vessels, and the collision came. There was no time to think—no time to act; there was a fearful cracking and tearing, during which it seemed that the Bywell Castle would walk right through the ill-fated pleasure-boat, and in that dread and awe-inspiring moment the startled eye saw its fate, and the happy heart was stilled in horror. Only five minutes from the time the vessels struck, and all that was then the Princess Alice lay cradled in the mud at the bottom of the Thames.
Save for the few who clambered on to the Bywell Castle, and the proportionately fewer who could swim ashore, the entire human freight was hurled into the black and fœtid river, or carried down in the cabins and saloon of the submerged sepulchre. How terribly was this proved when the wreck was raised! The unfortunate passengers were found packed together at the foot of the companion ladders with no time to move hand or foot, with no air to breathe, stifled where they stood.