Marine chronometer

“ Harrison's experience with the compensation pendulum of his clock now proved of service to him. He had proceeded to introduce a similar expedient in his proposed chronometer. As is well known to those who are acquainted with the nature of springs moved by balances, the stronger those springs are, the quicker the vibrations of the balances are performed, and vice versa; hence it follows that those springs, when braced by cold, or when relaxed by heat, must of necessity cause the timekeeper to go either faster or slower, unless some method could be found to remedy the inconvenience. ”

“ Undoubtedly "the detent," or, as it is usually termed, "the chronometer escapement," is the most perfect of any of our portable time measurers. Although the marine chronometer is in a sense a portable timepiece, still it is not, like a pocket watch, capable of being adjusted to positions. As we are all aware, the detent escapement is used in fine pocket watches, still the general feeling of manufacturers is not favorable to it. ”

“ Six days later — that is, on the 30th June — the Board of Longitude met, when Harrison was present, and produced the chronometer with which he had made the voyage to Lisbon and back. The minute states: "Mr. John Harrison produced a new invented machine, in the nature of clockwork, whereby he proposes to keep time at sea with more exactness than by any other instrument or method hitherto contrived, in order to the discovery of the longitude at sea ”

“ One of the most extraordinary things connected with Applied Science is the method by which the Navigator is enabled to find the exact spot of sea on which his ship rides. There may be nothing but water and sky within his view; he may be in the midst of the ocean, or gradually nearing the land; the curvature of the globe baffles the search of his telescope; but if he have a correct chronometer, and can make an astronomical observation, he may readily ascertain his longitude, and know his approximate position — how far he is from home, as well as from his intended destination. ”

“ This splendid reward for a method of discovering the longitude was offered to the world — to inventors and scientific men of all countries — without restriction of race, or nation, or language. As might naturally be expected, the prospect of obtaining it stimulated many ingenious men to make suggestions and contrive experiments; but for many years the successful construction of a marine time-keeper seemed almost hopeless. At length, to the surprise of every one, the prize was won by a village carpenter — a person of no school, or university, or college whatever. ”

“ Captain Proctor answered the First Lord from Spithead, dated May l7th, 1736, promising his attention to Harrison's comfort, but intimating his fear that he had attempted impossibilities. It is always so with a new thing. The first steam-engine, the first gaslight, the first locomotive, the first steamboat to America, the first electric telegraph, were all impossibilities!
This first chronometer behaved very well on the outward voyage in the Centurion. It was not affected by the roughest weather, or by the working of the ship through the rolling waves of the Bay of Biscay. ”

“ Indeed, it is amazing to think of the number of clever, skilful, and industrious men who have been engaged for many hundred years in the production of that exquisite fabric — so useful to everybody, whether scientific or otherwise, on land or sea the modern watch.
It is unnecessary here to mention in detail the particulars of Harrison's invention. These were published by himself in his 'Principles of Mr. Harrison's Timekeeper.' It may, however, be mentioned that he invented a method by which the chronometer might be kept going without losing any portion of time. ”

“ It was Quare who originated the practise of giving to each watch a serial number, so that it could always be identified. This is, of course, a common custom with us; we also number automobiles, and many other manufactured articles of value, and Quare's device of numbering watch-movements may very well have given the start to all this.
Still other famous watchmakers were Harrison and Arnold and Earnshaw, who between them developed and perfected the marine chronometer that we discussed in the last chapter; and Mudge, in whose hands watch-movements really became modern in type. ”

“ Every one knows the beautiful machinery of a timepiece, and the perfect tools required to produce such a machine. Some of these tools Harrison procured in London, but the greater number he provided for himself; and many entirely new adaptations were required for his chronometer. As wood could no longer be exclusively employed, as in his first clock, he had to teach himself to work accurately and minutely in brass and other metals. ”

“ The question of longitude is purely a question of TIME. The circuit of the globe, east and west, is simply represented by twenty-four hours. Each place has its own time. It is very easy to determine the local time at any spot by observations made at that spot. But, as time is always changing, the knowledge of the local time gives no idea of the actual position; and still less of a moving object — say, of a ship at sea. ”

“ It may here be mentioned that it was comparatively easy to determine the latitude of a ship at sea every day when the sun was visible. The latitude — that is, the distance of any spot from the equator and the pole — might be found by a simple observation with the sextant. The altitude of the sun at noon is found, and by a short calculation the position of the ship can be ascertained.
The sextant, which is the instrument universally used at sea, was gradually evolved from similar instruments used from the earliest times. ”

“ Notwithstanding the possibility that these exhibits might have been better prepared for observatory time tests, some of the exhibits, as will be seen by the rating, demonstrate the wonderful advances made in the application of horological sciences to the manufacture of watches, and that their rating is being made equal to that of the best marine chronometers.
The following is the report of Professor Russell, and the accompanying diagram (see next page) will readily give an idea of the comparative performance of the different watches. ”

“ But it must not be overlooked that in long voyages a chronometer, however perfect its construction, is more liable to get wrong than at a fixed station. That it is continually tossed and shaken is something, but is not the chief trial to which it is exposed. The great changes of temperature endured, when a ship passes from the temperate latitudes across the torrid zone to the temperate zone again, try a chronometer far more severely than any ordinary form of motion. ”

“ The chronometer, for finding longitudes, has taken the place of lunar observations, and the story of the struggle to invent a time-keeping mechanism of requisite accuracy for use at sea is one of the romances of science. Watches were unknown until 1530, but before the end of that century efforts had been made to ascertain the difference in time between two places by means of two of these crude timepieces which, however, were too unreliable to be of any practical service to navigation. ”

“ Try to imagine “All larboard bowlines on deck!” being shouted down into the forecastle of a present day ship. Yet that was the call used on the Pilgrim to fetch Dana and the rest of his watch on deck.
The chronometer, which is merely the least imperfect time-piece man has devised, makes possible the surest and easiest method by far of ascertaining longitude. Yet the Pilgrim sailed in a day when the chronometer was just coming into general use. So little was it depended upon that the Pilgrim carried only one, and that one, going wrong at the outset, was never used again. ”

“ 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. ”

“ Taking the case of a single chronometer, it has often to be relied on for months at a time, and during that period has probably to encounter many changes of temperature. If it gains or loses from day to day, and that consistently, it may still be accounted reliable, as the amount of error will be allowed for in all calculations. But should it gain one day and lose another, the accumulated errors would, on a voyage of several months, become so considerable as to imperil seriously the safety of the vessel if navigating dangerous waters. ”

“ Mulford, though I fancy you can say little on such a subject, that I have not often heard, already, from my poor, dear, Mr. Budd.”
This was not very encouraging, truly, but Rose continuing to look interested, the mate proceeded.
“The use of the chronometer is to ascertain the longitude,” said Harry, “and the manner of doing it, is simply this: A chronometer is nothing more nor less, than a watch made with more care than usual, so as to keep the most accurate time. They are of all sizes, from that of a clock, down to this which I wear in my fob, and which is a watch in size and appearance. ”

“ For behold, fourteen days later, in Suva, I compared the chronometer with the one on the Atua, an Australian steamer, and found that mine was thirty-one seconds fast. Now thirty-one seconds of time, converted into arc, equals seven and one-quarter miles. That is to say, if I were sailing west, in the night-time, and my position, according to my dead reckoning from my afternoon chronometer sight, was shown to be seven miles off the land, why, at that very moment I would be crashing on the reef. Next I compared my chronometer with Captain Wooley’s. ”

“ The chronometer mainly differs from the ordinary watch in being formed of a mixture of metals, which preserve so nice a chemical balance, that those changes of temperature which quicken or retard the movements of common time-pieces fail to affect it. Now, let us suppose that the friend and adviser of the sailor had said to him,—using a common metonymy,—there are no chronometers anywhere constructed that so completely neutralize the temperature as the ones I recommend to you ”

“ The truth was, having three excellent chronometers, one set to the time at Washington, one to that of Greenwich, and the other to that of Rio de Janeiro, and also an excellent watch daily regulated, which gave me the ship’s diurnal time accurately, I could easily calculate my longitude, and the point on which the sun ought to bear every hour in the 24. With these [81] calculations before me, I had but to look at my watch and the sun to determine my course. Thus in the longitude of Greenwich, when the chronometer set to Greenwich time stood at 12 o’clock noon, wherever the sun was, was north ”

“ Indeed no man has done more, none perhaps so much, towards removing the imperfections in chronometers, to which he alludes, as this great mechanician himself. His admirable time-piece, now in the possession of the Philosophical Society at Philadelphia, constructed by him, on an improved plan of his own, affords ample proof of the “astonishing accuracy” (as he expresses it) to which the pendulum-chronometer may be brought. A description of the mechanism of this extremely accurate time-piece, as well as of the principles on which its superior correctness depends, is inserted in the Appendix. ”

“ The sextant is the instrument (now greatly perfected) that is used to measure accurately the angles between the horizon and the celestial bodies being observed, and the chronometer is the accurate timepiece (now also greatly perfected) used on practically all sea-going ships to keep a record of the time of the prime meridian of longitude—that is, the meridian numbered zero. Usually, nowadays, that meridian, as I have said, is the meridian of Greenwich, England, for it is at Greenwich that a British observatory is located, and at this observatory the vital data for seamen are compiled. ”

“ The result from the chronometric expedition in 1855 previously referred to differing over a second of time.
In constructing charts for use at sea, the accurate determination of latitude and longitude is of the utmost importance. The navigator starting on a voyage must know the exact position of his destination as well as the location of dangers to be avoided. He must know the error and rate of his chronometer when he sets out, but as the rate is not constant he should have some means of re-rating it at any place where he may stop. ”

“ At the Royal Observatory, Greenwich, there are frequently above 100 chronometers being rated, and there have been as many as 170 at one time. They are rated daily by two observers, the process being as follows. At a certain time every day two assistants in charge repair to the chronometer-room, where is a time-piece set to true time; one winds up each with its own key, and the second follows after some little time and verifies the fact that each is wound. One assistant then looks at each watch in succession, counting the beats of the clock whilst he compares the chronometer by the eye ”

“ There was no chronometer on board the yacht, and he could not afford to buy one; so, as his watch was not to be depended upon, he saw that he would have to navigate his vessel after the fashion of the good old days before chronometers were known. The ancient navigators carried with them their astrolabes—rough instruments, long since superseded by quadrants and sextants—which enabled them to find their latitude accurately enough. But having no timepieces, they were unable to ascertain their longitude by observation of the heavenly bodies, and had to rely on dead reckoning alone. ”