by David Barrie
Imagine taking a sextant sight of a star from a position somewhere in the North Atlantic. If the star is vertically above you, your position must be identical with the star’s GP, which is easily determined by reference to the Nautical Almanac. So if you know the exact time, you can determine where you are without much trouble. If the star is not overhead, but, say, 45 degrees above the horizon, then you are somewhere on a very large circle with the star’s GP at its center—a circle consisting of all the points from which the star’s altitude at that moment measures 45 degrees. That is not much help, however, unless you can determine your exact position on that “equal-altitude” circle. Suppose then that you take a sight of another star, in a different part of the sky, at the same time. Once again, you will find yourself on a big circle, but these two equal-altitude circles will intersect—in two places. If you have made your observations correctly, it is simply a matter of deciding which of those two points makes better sense: one of them will be somewhere near your estimated position in the North Atlantic and the other will probably be thousands of miles away. Even if you know only your latitude, the choice should be clear.
In practice, you cannot easily reproduce such large imaginary circles on a paper chart, and if you did, the scale would be so small that it would be hard to determine your position accurately. However, as Marcq St. Hilaire demonstrated, there is no need to draw big circles.
The modern “intercept method” of celestial navigation is based on his insights. Having taken an accurately timed sight, the navigator chooses a place somewhere near to his or her DR position and works out what the height of the observed heavenly body ought to be if that “assumed position” were correct at the precise moment the sight was taken, as well as the true bearing (or azimuth) of the observed body’s GP from the assumed position. In Marcq St. Hilaire’s day it was necessary to calculate these values trigonometrically, but with the introduction of “sight-reduction” tables it became possible simply to look up the answers.* The difference between the precomputed altitude of the observed body shown in the tables and that derived from the actual observation (the “intercept”), coupled with the azimuth bearing, permits the navigator to draw a line on the chart: a line of position.6
This new graphical system was simpler than any of the older methods. No longer was there any need to calculate the local time and compare it with the time at Greenwich, nor was it necessary to determine the latitude. Moreover, useful sights could be taken at almost any time of day (or night). With the help of sight-reduction tables, you only had to add and subtract accurately and then plot the results on a chart.
Why it should have taken so long for this elegant, simplified technique to emerge is hard to say. Most books on the subject of marine navigation emphasize the great conservatism of sailors. Once they had learned how to do something, and provided it worked, they would doggedly go on doing it that way and would not trouble to seek improvements. There may be some truth in this generalization, but perhaps more important is the fact that few sailors were mathematically sophisticated. For most, celestial navigation was an arcane process that had to be learned by rule, and it would have required a high degree of self-confidence and mathematical skill to challenge the established system. These were qualities that Marcq St. Hilaire plainly had in abundance. He was to reach the rank of admiral but died in 1888 at the early age of fifty-eight. As one authority has written, his name “will always be remembered, so long as mariners practise the marvellous science which enables them to fix their ships with certitude and to rectify their courses with confidence.”7
UNDER COLIN’S GUIDANCE, I would take a sight of the sun in the morning (timed to the second with the aid of our chronometer) to obtain a single position line that ran roughly from northeast to southwest. A second sun sight in mid-afternoon would yield a position line running from northwest to southeast. Using DR to make allowance for the distance travelled between the two sights, I then “advanced” the first position line on the chart by the right amount and in the right direction: where the two lines crossed was our position. Now we knew both our latitude and our longitude, though neither value had been calculated directly. The same graphical procedure could then be repeated at twilight, making use of one or more of the “navigational” stars, the planets, or even the moon—details of which are listed day by day in the Nautical Almanac. By taking a number of sights almost simultaneously, the navigator can generate an immediate fix, in the form of a “cocked hat” of position lines.
Since an error of 1 minute (a mere sixtieth part of a degree) in the observed altitude will necessarily result in an error of one nautical mile in the position line, the whole process depends on the accuracy of the sextant sight itself. This was (and remains) largely a matter of skill and practice, though a good instrument and a clear sky (or at least a gap in the clouds) are obviously essential, as is a clear view of the horizon. In rough conditions—especially in a small vessel like a yacht—it is much harder to take a good sight. Experienced navigators can usually judge whether or not a single sight is good enough to be relied on, but to achieve the highest level of accuracy it is best to take a series of sights and plot them graphically—altitude against time. Deviant sights will then stand out clearly and can be discarded, while the arithmetic mean of the remaining ones is likely to provide a more reliable figure than any single sight.8
Accurate timekeeping is also crucial, but by the 1870s this was much less of a challenge than it had been when FitzRoy was serving in the Beagle forty years earlier. At that time the Royal Navy was only equipping its ocean-going vessels with “time-keepers”; since then the quality and reliability of marine chronometers had steadily improved and because prices had come down they were being employed increasingly widely. Well-equipped ships in the late nineteenth century usually carried at least three, so that by comparing their rates the navigator might more easily spot the discrepancies of any one instrument. The crucial developments, however, were the arrival of the electric telegraph and the laying of the first successful transoceanic cables in the 1870s and 1880s. Ports all around the world were now able to provide extremely accurate daily time signals (the dropping of a ball or the firing of a gun) for the rating of chronometers. These signals, which had first been introduced during the 1830s at a few major ports where observatories could keep accurate track of the time, offered a much more precise and simple way of checking the time than the old lunar-distance method. And in the early twentieth century, the introduction of radio time signals enabled the navigator to rate his chronometers wherever he happened to find himself—even far out at sea.
The “new navigation” was a major breakthrough and it marked the final stage in the development of celestial navigation. But it was a French discovery, and perhaps partly for that reason the British were slow to adopt it. Captain Lecky—whose wonderfully named Wrinkles in Practical Navigation (first published in 1881), with its salty language and charming illustrations, was for many years a bible for professional seamen—was frankly dismissive of the new technique.
He declared himself “averse to the diagram part of the method, which somehow seems . . . out of place in a ship.”9 Eventually, however, its merits became clear even to the most incorrigible Anglo-Saxons, and in the early years of the twentieth century it became the standard method taught to officers in the Royal Navy—among whom Colin was soon to be numbered.10
WHAT THEN HAPPENED to lunars? Lecky’s comments about lunars in my 1903 edition suggest that by then they were almost obsolete:
Once upon a time Lunars used to be the crucial test of a good navigator, but that was . . . when ships were made snug for the night, and the East India “Tea-waggons” took a couple of years to make the round voyage.
The writer of these pages, during a long experience at sea in all manner of vessels, from a collier to first-class Royal Mail steamer, has not fallen in with a dozen men who had themselves taken Lunars, or had ever seen others do so. Whether Lunars are worth cultivating or not may, in th
e minds of some people, still be open to question, but certain it is that they have fallen into disuse—are in fact as dead as Julius Caesar. . . .11
Dead they may have seemed to Lecky, yet some continued to cling to them. Of these perhaps the most famous was Joshua Slocum, whose book I read when sailing across the Atlantic in Saecwen. He was the first man to sail around the world single-handed—a feat he performed aboard the Spray, an old thirty-five-foot sloop that he had almost completely rebuilt with his own hands.
Slocum was born in 1844 on a small farm in Nova Scotia overlooking the Bay of Fundy and went to sea as a boy. I now realize that we must have passed very close to his birthplace when we sailed in Saecwen from Grand Manan Island, as well as following closely in his wake when we later departed from Halifax. Slocum learned his trade in sailing ships, starting as a deckhand and rising to become in 1881 master (and part owner) of “the magnificent ship Northern Light,” a large, three-masted clipper, which he proudly described as “the finest American sailing-vessel afloat.”12 This was the high point of his career and his “best command.” Slocum, accompanied by his wife and children, had many adventures aboard the Northern Light. They rescued Gilbert Islanders adrift in the Pacific,13 sailed through seas that were literally boiling close to the erupting volcano Krakatoa,14 and narrowly escaped sinking when the rudder was disabled in a gale off the coast of South Africa.15 But Slocum lost his command while defending himself in court against charges of cruelly treating an officer who had raised a mutiny against him. Though he was eventually vindicated, it was a murky episode.16 It did not, however, bring his career to an end: Slocum was to command several other ships before embarking on the retirement project that was to make him world famous.
Slocum set sail in the Spray from Gloucester, Massachusetts, in April 1895. He cruised up the coast of Maine to his home town of Westport before calling at Yarmouth on the southwest coast of Nova Scotia, where he laid in water and provisions and “stowed all under deck.”
At Yarmouth, too, I got my famous tin clock, the only timepiece I carried on the whole voyage. The price of it was a dollar and a half, but on account of the face being smashed the merchant let me have it for a dollar.17
Slocum had left behind his old chronometer—“a good one” that “had been long in disuse”—apparently because it was going to cost fifteen dollars to clean and rate it. “In our newfangled notions of navigation,” he complained, “it is supposed that a mariner cannot find his way without one; and I had myself drifted into this way of thinking.”18 But Slocum was to manage just fine without a chronometer. On July 2 the Spray sailed from Yarmouth and, after rounding Cape Sable, headed north before taking her departure from George’s Island, off Halifax, before dark on the evening of July 3:
I watched light after light sink astern as I sailed into the unbounded sea, till Sambro, the last of them all, was below the horizon. The Spray was then alone. . . . I raised the sheen only of the light on the west end of Sable Island, which may also be called the Island of Tragedies. The fog, which till this moment had held off, now lowered over the sea like a pall. I was in a world of fog, shut off from the universe. I did not see any more of the light.19
Slocum was a great showman and storyteller, so it would be unwise to take everything he wrote at face value, but there is no reason to doubt the main elements of his account in Sailing Alone Around the World. First he called at Horta in the Azores, and then Gibraltar, before he headed south down the Atlantic and—like so many before him—fought his way through the Straits of Magellan. Having “anchored and weighed many times” and after beating “many days against the current,” Slocum at last reached Port Tamar, with Cape Pillar in sight to the west. “Here I felt the throb of the great ocean that lay before me. I knew now that I had put a world behind me, and that I was opening out another world ahead.”20
Heading out into the Pacific beyond Cape Pillar, however, the Spray ran into very heavy weather:
There was no turning back even had I wished to do so, for the land was now shut out by the darkness of night. The wind freshened, and I took in a third reef. The sea was confused and treacherous. . . . “Everything for an offing,” I cried, and to this end carried on all the sail she would bear . . . but on the morning of March 4 the wind shifted to the southwest, then back suddenly to northwest, and blew with terrific force. . . . No ship in the world could have stood up against so violent a gale. . . .21
Slocum had no choice but to run before the wind, and so the Spray drove southeast, as though to round the Horn:
The first day of the storm gave the Spray her actual test in the worst sea that Cape Horn or its wild regions could afford, and in no part of the world could a rougher sea be found than at this particular point, namely, off Cape Pillar, the grim sentinel of the Horn.22
In these conditions Slocum could only trust to DR, and on the fourth day of the gale, when he thought he was nearing Cape Horn, he saw through “a rift in the clouds a high mountain, about seven leagues away on the port beam.” He now headed for the land, which appeared as an island in the sea: “So it turned out to be, though not the one I had supposed.” The weather was moderating, but the sea conditions were still bad and night closed in before the Spray reached the land, leaving Slocum to feel the way in “pitchy darkness.” He saw breakers ahead and stood offshore, but was “immediately startled by the tremendous roaring of breakers again ahead and on the lee bow.” He was puzzled, and no doubt alarmed, for there should have been no broken water where he supposed himself to be, and he must have realized that his navigation had gone seriously wrong. He stood off and on repeatedly, but each time he closed the coast he was confronted by breakers:
In this way, among dangers, I spent the rest of the night. Hail and sleet in the fierce squalls cut my flesh till the blood trickled over my face; but what of that? It was daylight, and the sloop was in the midst of the Milky Way of the sea, which is northwest of Cape Horn, and it was the white breakers of a huge sea over sunken rocks which had threatened to engulf her through the night. It was Fury Island I had sighted and steered for, and what a panorama was before me now and all around! . . . This was the greatest sea adventure of my life. God knows how my vessel escaped.23
Slocum was not exaggerating, as is evident from the description in the 1993 edition of the South America Pilot book, which uses the Spanish name for the Milky Way:
Via Láctea . . . so named because it is white with spume . . . consists of innumerable rocks, some above water, on which the sea continually breaks. This area, which includes Rocas Júpiter and Rocas Neptuno, should be avoided as it is little known and extremely dangerous.24
The Spray at last reached a safe anchorage behind some small islands that sheltered her in smooth water. Then Slocum climbed the mast to survey the wild scene astern:
The great naturalist Darwin looked over this seascape from the deck of the Beagle, and wrote in his journal, “Any landsman seeing the Milky Way would have a nightmare for a week.” He might have added, “or seaman” as well.25
Slocum was perhaps quoting from memory. Darwin’s actual words were even more awestruck: “One sight of such a coast is enough to make a landsman dream for a week about shipwrecks, peril, and death.”26 And we have already heard FitzRoy’s professional judgment of “Breaker Bay,” which lies close by. Slocum now returned to the relatively sheltered waters of the Straits of Magellan via the Cockburn Channel. If he was chastened by his narrow escape from shipwreck, the effects quickly wore off. Soon he was delighted by his success in defending himself from marauding Tierra del Fuegians. These he claimed to have discouraged by placing upturned carpet tacks across the Spray’s decks. Anything but politically correct, Slocum cheerfully boasted:
I had no need of a dog; they howled like a pack of hounds. I had hardly use for a gun. They jumped pell-mell, some into their canoes and some into the sea, to cool off, I suppose, and there was a deal of free language over it as they went.27
After many setbacks and delays, Slocum finally
escaped the confines of the Straits on April 13, 1896, and headed for the island of Juan Fernández, where he visited the cave of Alexander Selkirk, one of the inspirations for Defoe’s Robinson Crusoe. He found it “dry and inhabitable,” in a “beautiful nook” sheltered by high mountains.28 From there he sailed for the Marquesas Islands, 3,500 nautical miles to the north and west in the middle of the Pacific. It was some time before he picked up the trade winds, but
when they did come they came with a bang, and made up for lost time; and the Spray, under reefs, sometimes one, sometimes two, flew before the gale for a great many days, with a bone in her mouth. . . . My time was all taken up those days—not by standing at the helm; no man, I think, could stand or sit and steer a vessel round the world: I did better than that; for I sat and read my books, mended my clothes, or cooked my meals and ate them in peace. I had already found that it was not good to be alone, and so I made companionship with what there was around me, sometimes with the universe and sometimes with my own insignificant self; but my books were always my friends, let fail all else. . . .29
Slocum generally says little about his navigational methods, and it sounds as if he relied on DR (he admits to using a “rotator log”—just as we did in Saecwen) and latitude sailing for much of the time, but on this occasion it was his knowledge of lunars that enabled him to make a safe landfall. Day after day he sailed with a following wind, marking the position of the Spray on the chart more by intuition than “slavish calculations.” For a whole month his vessel held her course true without so much as a light in the binnacle. Every night he saw the Southern Cross shining out abeam. Every morning the sun rose astern and every evening it went down ahead of him. He wished for no other compass to guide him, as “these were true,” but at last he reached for his sextant: