When the Victoria [the only ship to return from Magellan’s famous voyage] reached the Cape Verde Islands, the sailors believed the day to be Wednesday, whereas it was Thursday. They had consequently lost one day on their voyage, and during their three years’ absence. I said:
Your priests must have deceived you, since they have forgotten this day in their ceremonies and the recitation of their office [prescribed religious service].' They answered: Of what are you thinking? Do you suppose that all of us, including wise and experienced men, could have made such a mistake? It often happens that an exact account is kept of the days and months, and moreover many of the men had office books and knew perfectly what had to be recited each day. There could be no mistake, especially about the office of the blessed virgin [Mary], at whose feet we prostrate ourselves each moment, imploring her assistance. Many passed their time reciting her office and that of the dead. You must, therefore, look elsewhere for an explanation, for it is certain that we have lost one day.’
Some gave one reason and some another, but all agreed upon one point, they had lost a day. I added: `My friends, remember that the year following your departure, that is to say, the year 1520, was a bissextile [leap] year, and this fact may have led you into error.’ They affirmed that they had taken account of the 29 days in the month of February in that year, which is usually shorter, and that they did not forget the bissextile of the calends of March of the same year. The 18 men who returned from the expedition are mostly ignorant, but when questioned, one after another, they did not vary in their replies.
Much surprised by this agreement, I sought Gaspar Contarino, ambassador of the illustrious Republic of Venice at the court of the emperor [Charles V]. He is a great sage in many subjects. We discussed in many ways this hitherto unobserved fact, and we decided that perhaps the cause was as follows:
The Spanish fleet, leaving the Gorgades [Cape Verde] Islands, proceeded straight to the west, that is to say, it followed the Sun, and each day was a little longer than the preceding, according to the distance covered. Consequently, when the tour of the world was finished-which the Sun makes in 24 hours from its rising to its setting the ship had gained an entire day; that is to say, one less than those who remain all that time in the same place. Had a Portuguese fleet, sailing towards the east, continued in the same direction, following the same route first discovered, it is positive that when it got back to the Gorgades it would have lost a little time each day, in making the circuit of the world; it would consequently have to count one day more. If on the same day a Spanish fleet and a Portuguese fleet left the Gorgades, each in the opposite direction, that is to say one towards the west and the other towards the east, and at the end of the same period and by different routes they arrived at the Gorgades, let us suppose on a Thursday, the Spaniards who would have gained an entire day would have called it Wednesday. The Portuguese who would have lost a day would declare it to be Friday. Philosophers may discuss the matter with more profound arguments, but for the moment I give my opinion and nothing more.