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you, envi-sioned, 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 for-tunately, 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 used it only to look at ships in port) and training
that instrument on the heavens. And there, among the many things that Father Caspar would not dream of
doubting, Galilei had discovered that Jupiter, or Jove, as he called it, had four satellites, that is to say four
moons, never seen from the beginning of the world until that moment. Four little stars that revolved
around it while it re-volved around the sun and we will see that for Father Caspar the idea that Jove
revolved around the sun was admissible, provided the earth was left alone.
Now, it is a well-known fact that our moon, when it passes in the shadow of the earth, is eclipsed.
Astronomers have long known when lunar eclipses would occur, and the ephemerides were authoritative.
It was not surprising, then, that the moons of Jove also had their eclipses. Indeed, for us at least, they had
two, one actual eclipse and one occultation.
In fact, the moon disappears from our sight when the earth comes between it and the sun, but the
satellites of Jove dis-appear from our sight twice, when they pass behind it and when they pass in front,
becoming united with its light; through a good spyglass you can easily follow their appear-ances and their
disappearances. With the inestimable advantage that while the eclipses of the moon occur only very
rarely and take a long time, those of the Jovian satellites occur fre-quently and are rapid.
Now let us suppose that the hour and the minutes of the eclipses of each satellite (each traveling in an
orbit of different breadth) have been precisely established on a known meridian, and the ephemerides
bear this out; at which point it is enough to be able to fix the hour and the minute when the eclipse is
visible on the (unknown) meridian, and the calculation is quickly made, and the longitude of the point of
observation can be deduced.
True, there were minor drawbacks, not worth discussing with a layman, but the enterprise would
succeed for a good calculator who had at his disposal a measurer of time, namely a perpendiculum or
pendulum, or Horologium Oscillatorium as might be, capable of measuring with absolute precision even
to the second. Similarly, he would need two normal clocks that told him faithfully the hour of the
beginning and the end of the phenomenon both on the meridian of observation and on that of the Isla de
Hierro; and, using the table of sines, he could measure the quantity of the angle made in the eye by the
bodies under examination the angle that, if thought of as the hands of a clock, expressed in minutes and
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seconds the distance between the two bodies and its progressive vari-ation.
Provided, it is well to repeat, he also had those good eph-emerides that Galilei, by then old and infirm,
had not been able to complete, but that the brethren of Father Caspar, already so good at calculating
eclipses of the moon, had now perfected.
What were the chief flaws, over which Galilei s adversaries had waxed so bitter? That these
observations could not be made with the naked eye and the observer needed a strong spyglass, or
telescope, as it was now more properly called? And Father Caspar had some of excellent facture such as
not even Galilei had dreamed of. That the measuring and the calculat-ing were not within the skill of
sailors? Why, all the other methods for determining longitude, except perhaps the log, required the
presence of an astronomer! And if captains had learned to use the astrolabe, which itself was not
something within the grasp of any layman, they could also learn to use the glass.
But, the pedants said, such exact observations requiring great precision could perhaps be made on land,
but not on a ship in motion, where no one could hold a glass fixed on a celestial body invisible to the
naked eye.... Well, Father Caspar was here to demonstrate that, with a bit of skill, ob-servations could
be made also on a moving ship. [ Pobierz całość w formacie PDF ]