What of the loch or the navicella, or whatever you choose to call it? The usual ones do not work, but here is what Father Caspar had constructed: a box with two vertical poles, one that wound as the other unwound a cord of fixed length equivalent to a fixed number of miles; and the winding pole was surmounted by many little blades, which as in a mill turned under the force of the same winds that swelled the sails: their movement accelerated or slowed—and therefore wound or unwound the cord—according to the strength and direction, straight or oblique, of the wind, recording meanwhile also the deviations due to tacking, or sailing against the wind. A method not much more sure than all the others, but excellent if someone compared its results with those of other soundings.
Lunar eclipses? To be sure, observing them during a voyage resulted in endless misunderstandings. But what about those observed on land?
“We must have many observers and in many places of the world, and well disposed to collaborate in the major glory of God, and not exchange insults or spitefulness or scorn. Listen: in 1612, the eighth of November, at Macao, the most reverend pater Iulius de Alessis records an eclipse at eightthirty that evening until eleven-thirty. He informs the most reverend pater Carolus Spinola, who at Nangasaki, in Iaponia, the same eclipse at ninethirty of the same evening was observing. And the pater Christophorus Schnaidaa had the same eclipse seen at Ingolstadt at five in the afternoon.
The differentia of one hora makes fifteen degrees of meridian, and therefore this is the distance between Macao and Nangasaki, not sixteen degrees and twenty, as says Blaeu. Verstanden? Naturally with these records you must guard against drink and smoke, have correct horologii, not lose the initium totalis immersionis, and maintain correct medium between initium and finis eclipsis, observe the intermediary moments in which the spots are dark, et cetera. If the places are distant, a very little error makes no gross differentia, but if the places are proximi, an error of a few minutes makes gross differentia.”
Apart from the fact that in the matter of Macao and Nagasaki it seems to me that Blaeu is closer to the truth than Father Caspar (which proves how complicated longitudes were at that time), this is how the Jesuits, after collecting and collating the observations of their missionary brethren, established a Horologium Catholicum, which—despite the name—was not a clock devoted to the Roman pope but a universal clock. It was in effect a kind of planisphere on which were marked all the headquarters of the Society, from Rome to the borders of the known world, and for each place the local time was marked. Thus, Father Caspar explained, he had not had to bear in mind the hour at the beginning of the voyage but only at the last outpost of the Christian world, whose longitude was beyond debate. Then the margins for error were greatly reduced, and between one station and the next they could also use methods that, in the absolute sense, offered no guarantee, such as the variation of the needle or calculation from lunar spots.
Fortunately he had brethren just about everywhere, from Pernambuco to Goa, from Mindanao to Porto Sancti Thomae, and if winds prevented the Daphne from mooring in one port, there would soon be another. For example, at Macao … ah, Macao! At the very thought of that adventure, Father Caspar glowered. It was a Portuguese possession; the Chinese called the Europeans men of long noses precisely because the first to land on their shores were the Portuguese, who truly do have long noses, and also the Jesuits, who came with them. So the city was a single garland of blue and white fortresses on the hill, controlled by the fathers of the Society, who had to concern themselves also with military matters, since the city was threatened by the Dutch heretics.
Father Caspar had decided to head for Macao, where he knew a fellow Jesuit very learned in the astronomical sciences, but he had forgotten that he was sailing on a fluyt.
What did the good fathers of Macao do? Sighting a Dutch ship, they manned their cannons and colubrines. In vain Father Caspar waved his arms at the prow and immediately had the Society’s standard run up; those cursed long-noses, his Portuguese brothers in the Society, wrapped in the warrior smoke that invited them to a holy massacre, did not even notice, and they rained balls around the Daphne. It was the pure grace of God that the ship was barely able to strike its sails, come about, and escape to sea while the captain in his Lutheran language hurled anathema at those fathers of scant consideration. And this time he was right: sinking the Dutch is all very well, but not when there is a Jesuit on board.
Luckily it was fairly easy to reach other missions not far away, and they turned their bowsprit towards the more hospitable Mindanao. And so, from one port to the next, they kept watch over their longitude (and God help them, I add, considering that, having ended up practically in Australia, they must have lost track of every point of reference).
“Et hora we must novissima experimenta make, ut clarissime et evidenter demonstrate that we are on meridian one hundred eighty.
Otherwise the fratres of the Collegium Romanum will think I am a Mamelukke.”
“New experiments?” Roberto asked. “Did you not just tell me that the Specula gave you the utmost assurance of being on the one-hundredeightieth meridian, off the Island of Solomon?”
Yes, the Jesuit replied, he was certain: he had set in competition the various imperfect methods found by others, and the accord of all these weak methods supplied a very strong certitude, as happens in the proof of God’s existence by consensus gentium, for while it is true that many men inclined to err also believe in God, it is impossible that all should be mistaken, from the forests of Africa to the deserts of China. So it happens that we believe in the movement of the sun and the moon and of the other planets, or in the hidden power of Chelidonium, or that at the center of the earth there is a fire; for thousands and thousands of years men have believed these things, and while believing them, they have been able to live on this planet and achieve many useful results from their reading of the great book of Nature. But an important discovery like this had to be confirmed by further proof, so that even the sceptics would surrender to the evidence.
Besides, science must be pursued not only for the love of learning but in the desire to share it with our brothers. So, since it had cost him such an effort to find the correct longitude, he now had to seek confirmation through other, easier methods, so that this knowledge could become the patrimony of all our brothers, “or at least of the Christian ones, or, rather, the Catholic brothers, because, as for the Dutch or English heretics—or worse, the Moravians—it would be far better if they never came to learn of these secrets.”
Now, of all the methods of taking longitude, two seemed sure to him. One, good for terra firma, was that treasure of all methods, namely the Specula Melitensis; the other, appropriate for observation at sea, was the Instrumentum Arcetricum, which lay below but had not yet been set up, because he first had to obtain through the Specula the certitude of their position, then see if the Instrumentum confirmed it, which was the most reliable way to proceed.
Father Caspar would have carried out this experiment long before if what happened had not happened. But the moment now had come, and it would be on that very night: the sky and the ephemerides said that now was the right occasion.
What was the Instrumentum Arcetricum? A device envisioned many years earlier by Galilei—but, mind you, envisioned, narrated, promised, never achieved, until Father Caspar set to work. When Roberto asked him if that Galilei was the same who had advanced a severely condemned hypothesis about the motion of the earth, Father Caspar replied yes, when that Galilei had stuck his nose into metaphysics and the Sacred Scriptures, he had said dreadful things, but as a mechanical he was a man of genius and very great. Asked whether it was not wrong to use the ideas of a man the Church had censured, the Jesuit answered that to the greater glory of God the ideas of a heretic also could contribute, provided they in themselves were not heretical. And we might have known that Father Caspar, who welcomed all existing methods, not swearing by any one of them but exploiting their quarrelsome conference, would exploit also the method of Galilei.
Indeed, it was highly useful both for science and for the faith to develop as soon as possible that idea of Galilei; the Florentine himself had tried to sell it to the Dutch, but fortunately, like the Spaniards a few decades earlier, they did not trust him.
Galilei had drawn some odd conclusions from a premiss that in itself was quite right, namely that of stealing the idea of the spyglass from the Flemings (who
