Sextant
Page 20
FitzRoy brought no fewer than twenty-two chronometers with him—many of which he paid for himself—as well as an instrument maker whose sole function was to maintain them. In keeping with well-established practice, however, he methodically checked their performance at every opportunity by astronomical means. By the time the Beagle returned home in October 1836, some of the watches had stopped, others had exhibited sudden changes of rate, and the mainspring of one had broken when it had been “going admirably.”26 Only half of the original twenty-two were still in good order. So even at this stage in the development of the watchmaker’s art the chronometer was not an instrument on which a ship’s captain could rely with complete confidence.
During the four-year voyage of the Beagle, FitzRoy and his colleagues gathered abundant information about tides, ocean currents, weather patterns, earthquakes, mountain ranges, isolated reefs, fossils, animal and plant species, the structure of coral atolls, and much else besides—including the customs of the many different native populations they encountered. These discoveries, in Darwin’s hands, were to inspire the epoch-making theory of evolution by natural selection and gravely undermine traditional religious beliefs—greatly to FitzRoy’s dismay. From the point of view of the Admiralty, however, the most valuable product of the voyage was the mass of navigational data that FitzRoy had gathered with the help of his sextants and chronometers.
For all the technological progress that had been made, navigation still remained a perilous business—as an episode early on in the Beagle’s circumnavigation makes clear. While on the coast of Brazil, FitzRoy made a point of investigating the disturbing loss of the crack frigate Thetis (in which he had earlier served) on the bold headland of Cape Frio, about seventy miles east of Rio de Janeiro. The court-martial proceedings, which FitzRoy quotes in his journal, give a dramatic account of the wreck. The Thetis had set sail from Rio in foggy weather on December 4, 1830, first heading out to sea and then shaping a generally eastward course parallel with the coast. By 4 P.M. the following day, relying on DR “as neither sun, moon or stars had been seen,” it was reckoned that the ship was twenty-four miles off the Cape and her course was altered accordingly to northeast by east. After a brief clearing when—reassuringly—no land could be seen, “thick and rainy” weather set in and by 8 P.M. “nothing could be distinguished half a ship’s length distant”:
Soon after eight one of the look-out men . . . said to another man on the forecastle, “Look how fast that squall is coming” . . . and next moment, “Land a-head,” “Hard a-port,” rung in the ears of the startled crew, and were echoed terribly by the crashing bowsprit, and thundering fall of the ponderous masts.
The hull did not immediately strike the rocks, as the ship answered the helm very quickly, but as she turned the bowsprit broke and the lee yardarm irons “struck fire from the rocky precipice” as they grated harshly against it, while the boom ends snapped off “like icicles.”
All three masts fell . . . strewing the deck with killed and wounded men. An immense black barrier impended horribly, against which breakers were dashing with an ominous sound; but the ship’s hull was still uninjured. Sentries were placed over the spirit-room; a sail was hoisted upon the stump of the main-mast; the winches were manned; guns fired; rockets sent up, and blue-lights [fireworks used as distress signals] burned. . . .27
The boats were cleared away for lowering and an anchor was let go, but the water was so deep that before the anchor could grip the ship’s stern drifted onto a shelving rock. Some of the crew then tried to jump ashore, but many slipped and were drowned in the surf, or crushed against the rocks. The ship was now starting to sink and successive waves threw her stern on the rocks. Luckily the battered ship was then driven into a small cove, and by daylight all the survivors were saved by being hauled through the surf along a rope stretched to the shore. Many, however, were terribly bruised and lacerated, and twenty-five had lost their lives. Some of the officers obtained horses, and a guide took them back to Rio de Janeiro, where “the melancholy news was communicated to the commander-in-chief.”
The loss of such a large quantity of treasure, as well as a fine ship and many men, no doubt added to the sense of dismay evoked by this disaster. There could hardly be a clearer demonstration of the unreliability of DR, but FitzRoy was anxious to establish how such a serious navigational error could have occurred within just nineteen hours of the Thetis setting sail from Rio. Skeptical of the theory that the accident had been caused by a local magnetic disturbance affecting the steering compass, he concluded that the Thetis had been pushed off course by a strong but hitherto unknown seasonal current setting the ship to the north. His conclusion was generous, and wry:
If a man of war is accidentally lost, a degree of astonishment is expressed at the unexpected fate of a fine ship, well found, well manned, and well officered; and blame is imputed to some one: but before admitting a hastily-formed opinion as fact, much inquiry is necessary.
. . . Those who never run any risk; who sail only when the wind is fair; who heave to when approaching land, though perhaps a day’s sail distant; and who even delay the performance of urgent duties until they can be done easily and quite safely; are, doubtless, extremely prudent persons:—but rather unlike those officers whose names will never be forgotten while England has a navy.28
Even if FitzRoy had died in 1836, his own name would deserve a place in that illustrious list. But a varied and distinguished career still lay ahead of him. Soon after his return, he married and published his account of the Beagle voyages. Having been elected a member of Parliament in 1841, he turned his back on a potentially successful political career by accepting a posting as governor of New Zealand in 1844. The infant British colony was then in the throes of bitter disputes both among the European settlers and between them and the native Maori population. FitzRoy lacked the necessary resources, both financial and military, to manage the situation successfully, but his conciliatory approach to the Maoris—born of his increasingly fervent Christian beliefs—was exemplary. Party political maneuvering in London was largely responsible for his early recall in 1845, after which he returned to active service as commander of the Royal Navy’s first propeller-driven frigate. But having suffered a crippling bout of depression, brought on in part by growing financial problems, FitzRoy resigned his command in 1850. He was never offered another.
Some of FitzRoy’s greatest achievements came at the end of his career. Building on his own experience and detailed observations at sea, and those of other scientifically minded mariners like Flinders, he played an important role in the development of meteorological science. In 1854 he became the first head of what is now known as the Meteorological Office. In that role, and in the teeth of bureaucratic obstruction and ill-informed public criticism, he established in 1861 a pioneering system of “storm warnings” based on data gathered telegraphically from observation stations around the United Kingdom. He invented the visual signals (“storm cones”) that were hoisted at the entrance of ports to warn ships of approaching heavy weather, and they were soon replicated in other countries. Though briefly suspended after his death, this “storm warning” system remained in place for many years. He also designed a robust barometer that was issued as standard to ships, with an instruction manual that would enable the commander to foretell likely changes in the weather.29 FitzRoy went on to develop the first “weather forecasts”—a term that he himself coined—and in 1862 published a popular work on meteorology, The Weather Book. Though some of the ideas he put forward have not stood the test of time, his researches enabled him to recognize the existence of ridges and troughs, as well as wider areas of low and high atmospheric pressure, all key determinants of the weather.30
An episode recounted in The Weather Book dramatically illustrated the value of barometric readings at sea. On FitzRoy’s return voyage from New Zealand in 1846, the ship in which he and his family were sailing anchored at the western end of the Straits of Magellan—a part of the world that he
knew better than most. The weather was fair and the ship’s captain seemed content to spend the night riding to a single light anchor, but FitzRoy, having noticed that his two personal barometers were dropping sharply, remonstrated with him. The captain agreed to replace the light anchor with a heavier one and to reduce the ship’s windage by striking some of her lighter spars down to the deck, but the barometers continued to fall and, the captain now being peacefully asleep in his bunk, FitzRoy persuaded “a good officer and a few willing men” to drop a second anchor, even though the night as yet remained calm. At 2 A.M. the storm he had predicted hit the ship and, despite all the precautions, she dragged her anchors to “within a stone’s throw of sharp granite rocks astern, at some distance from land, near the most exposed outer point of the harbour.” But for FitzRoy’s intervention she would almost certainly have been lost.31
The publication in 1859 of Darwin’s revolutionary work On the Origin of Species deeply disturbed FitzRoy, who was by now convinced of the literal truth of the Genesis story. He felt personally responsible for the shocking ideas expressed in the new book because Darwin had been sailing with him when carrying out the research that inspired them. His few attempts to combat Darwin’s ideas were, as he himself realized, quite futile. Though he reached the rank of vice admiral in 1863, he was by then worn-out by a lifetime of hard work. Depression once again gripped him. Dismayed by the apparently unstoppable progress of Darwinism, worried by his worsening financial problems, and hurt by criticism (much of it unfair) of his meteorological endeavors, in 1865 he cut his throat—just as his uncle Lord Castlereagh had done in 1822.
It was a heartbreaking end to a remarkable career. The Hydrographer of the Navy, George Richards, wrote to FitzRoy’s widow that “No naval officer ever did more for the practical benefit of navigation and commerce than he did, and did it too with a means and at an expense to the country that would now be deemed totally inadequate. . . . His works are his best as they will be his most enduring monument, for they will be handed down to generations yet unborn.” Despite their differences, even Darwin acknowledged in his autobiography that FitzRoy’s character had “many noble features,” declaring that “he was devoted to his duty, generous to a fault, bold, determined, indomitably energetic, and an ardent friend to all under his sway.”32
Though not at first fully appreciated, FitzRoy’s contributions to the science and practice of meteorology, and to the welfare of mariners, were at last publicly recognized in 2002 when the BBC Shipping Forecast area Finisterre was renamed “FitzRoy.” It is the only sea area named after an individual.
Chapter 15
Slocum Circles the World
Day 16: Wind and seas at last down. N force 3—full main again and No. 1 stays’l making 6 knots.
During morning accompanied again by dolphins. One jumped clear of the water within a few feet and seemed to look right at me. It is very strange how everyone responds to them—we all stood at the bows watching them and laughing with delight. They really seem to be aware of our presence, and they move with such astonishing ease and grace. Perhaps we envy their freedom and their ability to make their home out here where we can live only on sufferance.
Overcast skies and quite cold. Noon position 45°32' N, 25°34' W. Lunch of soup, Ryvita, corned beef and Dundee cake. Colin put a message in an empty whisky bottle giving his address and offering a reward of £5 to the finder for reporting its discovery. Pretty tired, but we’re making good progress.
At 1530 the wind backed to NW and eased so we hoisted the big blue genoa again and trickled along at 3–4 knots. More star sights.
Day 17: A good night’s rest and up at 0400 to see the dawn and finished Slocum.
Slept after breakfast until Alexa called out that a ship was approaching. She was a smart white general cargo vessel and she came past quite close by on the same course at full speed with the crew lining the rail and waving. Even better Colin managed to make contact on the radio-telephone. The operator was very efficient and helpful giving us the weather forecast (SW 3, 4) and asking our destination and ETA. He promised to report us to Lloyd’s.* She was the “Tanamo”—Dutch and registered in Rotterdam, bound for Cork.
Combined with suddenly clear skies and a warm sun, this encounter really cheered us. The rest of the day we had a fabulous broad reach at 6½ in S’thly force 3 winds. I even put on my shorts again.
At 1300 I worked out our position on my own again: 46°32' N, 23°57' W. This matched Colin’s results pretty closely. Course 090°.
In evening we had cannelloni for dinner and put our watches on an hour. Colin got out his squeeze box and Alexa her guitar and we had another boozy sing-song.
The position-fixing methods employed by FitzRoy differed hardly at all from those first developed in the middle of the eighteenth century, though the accuracy of the ephemeris tables had steadily improved. A year after the Beagle returned home in 1836, however, a fortuitous discovery by an American merchant seaman named Sumner1 led eventually to the development of a completely new approach to celestial navigation.
I first heard the name Sumner when I was helping to deliver a beautiful old yawl called Wester Till from Gare Loch on the west coast of Scotland to Brixham on the south coast of England. Our course took us down the Irish Sea and past the Smalls Lighthouse, which marks a dangerous, low-lying reef some thirteen nautical miles off the island of Skomer on the Pembrokeshire coast.* We could see the tall lighthouse clearly, and by measuring its height with the sextant we were able to determine our distance from it and our position. As the lighthouse receded from us, the yawl’s owner mentioned that Captain Thomas Sumner had discovered the principle of the “line of equal altitude,” on which modern celestial navigation depends, in just this patch of sea. In December 1837 Sumner was in command of a sailing ship bound from Charleston, South Carolina, to the Clyde. The standard method of fixing a ship’s position at that date was to deduce the longitude by comparing Greenwich time (recorded by the chronometer) with local time at the ship, and to couple this with the latitude, usually derived from a mer alt. However, the accurate calculation of local time by sextant sight depended on knowing the exact latitude. If for any reason the latitude was unknown, an accurate longitude could be obtained only by taking a sight of the sun when it bore precisely due east or due west, and this might well be impractical.
After passing the meridian of 21 degrees West (several hundred miles out into the Atlantic), Sumner—who was planning to reach the Clyde from the south, via the Irish Sea—was unable to take any sights until the DR suggested that he was within forty miles of the Tuskar Rock lighthouse, off the southeastern tip of Ireland. The wind hauled into the southeast and rose to gale force, while Sumner struggled to keep the ship on the same station until daylight. It was a tense and no doubt chilly night, as his position was uncertain and the lee shore of the Irish coast might be dangerously near. At break of day Sumner would have been relieved to find that no land was in sight, and at 10 A.M. he at last managed to snap a single sight of the sun, noting the time by chronometer. His latitude (52 degrees North) was highly uncertain, as it depended on DR. Using this figure, however, he obtained the local time and calculated that the ship was 15 minutes east of her DR position—nine nautical miles in that latitude. He then tried the calculation again using an assumed latitude 10 minutes farther north, and this placed him 27 miles ENE of the former position. Another calculation based on a latitude 10 minutes still farther to the north yielded a position 54 miles ENE of the first position. These three positions, he soon realized, all lay on a straight line passing through the Smalls Light off the Pembrokeshire coast:
It then at once appeared, that the observed altitude must have happened at all the three points, and at the Small’s light, and at the ship, at the same instant of time; and it followed that the Small’s light must bear E.N.E. if the chronometer was right. Having been convinced of this truth, the ship was kept on her course E.N.E., the wind bearing still S.E., and in less than an hour, Small’s
light was made, bearing E.N.E. ½ E. and close aboard.2
The straight line formed by the three points was a line of equal altitude. Sumner’s account of his accidental discovery appeared in 1843 and was quickly noticed by Royal Navy lieutenant Henry Raper—author of the standard work The Practice of Navigation. In an article published a year later, Raper described Sumner’s method of deriving a position line from a single sight as “highly ingenious and very useful when a ship is near land.”3 In due course, however, a number of brilliant French sailors and mathematicians were able to develop and systematize Sumner’s insight and thereby bring celestial navigation to perfection.
A week out of Halifax I was already fairly proficient at taking a mer alt and calculating our latitude from it. What we really needed, however, was not a line but a point: our actual position in the middle of the ocean. The method that Colin taught me was inspired by the French naval officer Adolphe Marcq St. Hilaire. The grandson of a senior naval officer who had died fighting the British in 1795, Marcq St. Hilaire was born in 1832 and won a scholarship to the Collège Royal in Cherbourg. He then moved on in 1847 to the École Navale (naval college), where the commanding officer recognized his great aptitude. Having joined the navy, he was posted to the Pacific, where he undertook hydrographic work for which he was highly commended.
Fig 8: Sumner Line.
Marcq St. Hilaire saw service at sea in many parts of the world but in 1870 returned to France in poor health and devoted himself to developing Sumner’s position-line method. In 1875, while serving aboard a training ship at Brest, in northwest France, he published a long article describing the new technique that bears his name.4 Building on the work of a naval colleague, Lieutenant Hilleret, Marcq St. Hilaire devised a novel and elegant solution so radical that he boldly called it the “new navigation.”5