“Did he make a mistake or did Regiomontanus?” the Knight asked.
“Who knows? On a ship, which moves constantly even when it is at anchor, it is always hard to take bearings correctly. You may also know that Columbus wanted to prove at all costs that he had reached Asia, and therefore his wish led him to err, to show he had gone much farther than he really had…. And lunar distances? They have been very fashionable over the last hundred years. The idea had—how shall I say—a certain wit. During its monthly course the moon makes a complete revolution from west to east against the sky of the stars, and therefore it is like the hand of a celestial clock that moves over the face of the Zodiac. The stars move through the sky from east to west at about fifteen degrees per hour, whereas during the same period the moon moves fourteen and a half degrees. So the moon, with respect to the stars, is off by half a degree each hour. Now the ancients thought that the distance between the moon and a fixed star, as it is called, was the same for any observer from any point on the earth. So it sufficed to know, thanks to the usual tables or ephemerides, and observing the sky with the astronomer’s Cross—”
“The staff?”
“Exactly, with this ‘Jacob’s Cross’ you calculate the distance of the moon from that star at a given hour on the meridian of departure, and you know that at the hour of observation at sea, in such and such a city it is a certain hour. But … ah…” And Byrd paused, to enthrall his listeners even more. “There are the parallaxes, a highly complex matter I dare not explain to you. They are due to the difference of refraction of the celestial bodies at different altitudes above the horizon. Now with these parallaxes the distance found here would not be the same that our astronomers back in Europe would find.”
Roberto remembered having heard from Mazarin and Colbert something about parallaxes, and about that Monsieur Morin who thought he had found a way of calculating them. To test Byrd’s knowledge, he asked if astronomers could not calculate parallaxes. Byrd replied that it was possible but extremely difficult, and the risk of error was very great. “And besides,” he added, “I am but a layman and know little of these things.”
“So the only thing is to seek a surer method?” Roberto then ventured.
“You know what your Vespucci said? He said: ‘As for longitude, it is a very perplexing thing that few people understand, except those capable of sacrificing sleep to observe the conjunction of the moon and the planets.’ And he said: ‘It is for this determination of longitudes that I have often renounced sleep and have shortened my life by ten years….’ A waste of time, I say. But look, the sky is overcast so let us hasten to our lodging, and end our talk.”
Some evenings later, Roberto asked the doctor to point out the Pole Star to him. The doctor smiled: from that hemisphere it could not be seen, and other fixed stars had to be used. “Another defeat for the seekers of longitudes,” he remarked. “This way, they cannot fall back even on the variations of the magnetic needle.”
Then, at the urging of his friends, he broke again the bread of his learning.
“The needle of the compass should always point north, and therefore in the direction of the Pole Star. And yet, except on the meridian of the Isla de Hierro, in all other places it shifts from true north, moving now east, now west according to the climes and the latitudes. If, for example, from the Canaries you move towards Gibraltar, as any sailor knows, the needle turns more than six degrees of a rhomb towards north-west, and from Malta to Tripoli there is a variation of two thirds of a rhomb to the left, and you well know that the rhomb is one fourth of a wind. Now these deviations, it has been said, follow set rules according to the different longitudes. So with a good table of deviations you could know where you are. But…”
“Another but?”
“Yes, unfortunately. There are no good tables of the declinations of the magnetic needle. Those who attempted to make them all failed, and there are good reasons to suppose that the needle does not vary in a uniform way depending on the longitude. Furthermore, these variations are very slow, and at sea it is difficult to follow them, even when the ship is not pitching and thus disturbing the balance of the needle. Whoever trusts the needle is a madman.”
Another evening, at supper, the Knight, brooding on a few words Roberto had let fall with apparent nonchalance, said that perhaps Escondida was one of the Solomons, and he asked if they were close.
Byrd shrugged. “The Solomon Islands! £a n’existe pas!”
“Did not the English Francisco Drako reach them?” the Knight asked.
“Nonsense! Drake discovered New Albion, in quite a different place.”
“The Spaniards at Casale spoke of it as something well known, and said they had been the discoverers,” Roberto said.
“It was that Mendaña who made the claim, some seventy years ago. But he said they lay between the seventh and eleventh degrees of latitude south. As if to say between Paris and London. But at what longitude? Queiros said that they were fifteen hundred leagues from Lima. Ridiculous. You could practically spit from the coast of Peru and hit them. Recently a Spaniard said that they lay seven thousand five hundred miles from that same Peru. Too far, perhaps. But be so kind as to look at these maps, some of them newly revised, though they but reproduce the older ones, as well as some offered to us as the latest discovery. You see? Some put the islands on the two-hundred-and-twelfth meridian, others on the two-hundred-andtwentieth, others on the two-hundred-and-thirtieth, not to mention those who imagine them on the hundred-and-eightieth. Even if one of these was right, others would err by as much as fifty degrees, which is more or less the distance between London and the lands of the Queen of Sheba.”
“It is truly admirable, the number of things you know, doctor,” the Knight said, answering the prayers of Roberto, who was about to say as much himself. “As if for your whole life you have done nothing but look for longitudes.”
Dr. Byrd’s face, dotted with pale freckles, suddenly flushed. He filled his mug with beer, drained it without taking a breath. “Oh, a naturalist’s curiosity. Actually, I would have no idea where to begin if I had to tell you our present position.”
“But…” Roberto thought he could speak up at this point. “By the tiller, I saw a chart on which—”
“Oh, yes.”—the doctor quickly recovered himself—”to be sure, a ship does not proceed at random. They prick the Card. They record the day, the direction of the needle and its declination, the direction of the wind, the hour of the clock on board, the miles traveled, the height of the sun and of the stars, and therefore the latitude, and from that they deduce a longitude. You will have seen sometimes at the poop a sailor throwing a rope into the sea with a little piece of wood attached to one end. It is the loch or, as some call it, the Dutchman’s log. The rope is let out, knotted at intervals for measurement, then with a clock you can calculate how much time it takes to cover a given distance. In this way, if everything proceeds regularly, you can determine how many miles you have sailed from the last known meridian.”
“You see? There is a method!” Roberto said triumphantly, already knowing what the doctor would reply. That the loch is something that is used only because there is nothing better, since it tells us how far a ship has gone only if it is proceeding in a straight line. But since a ship goes as the winds choose, when the winds are not favoring, it must move now to starboard, now to port.
“Sir Humphrey Gilbert,” the doctor said, “more or less at the time of Mendaña, in the Terranova region, intending to proceed along the fortyseventh parallel, ‘encountered winds always so scant,’ winds—how shall I say it?—so lazy and frugal, that for a long time he sailed anywhere between the forty-first and the fifty-first, ranging over ten degrees of latitude, gentlemen, which would be as if an immense snake were to go from Naples to Portugal, first touching Le Havre with its head and Rome with its tail, then finding itself with its tail at Paris and its head at Madrid!
So the deviations must be calculated before doing the sums, and one must be very careful—which a sailor never is. And you cannot have an astronomer ready at your side all day long. To be sure, estimates are possible, especially if you are following a familiar course and consider all the discoveries previously made by others. For this reason from the shores of Europe to those of the Americas the maps give meridians that are fairly reliable. And then, observation of the stars from land can produce some good results, and therefore we know the longitude of Lima. But even in this case, my friends,” the doctor asked gaily, “what happens?” And he looked slyly at the other two.
“It happens that this gentleman,” and he tapped a finger on one of the maps, “places Rome on the twentieth degree east
