‘But as to the size of the earth, even the great Ptolemy is only one authority among a range with differing views. Centuries before Ptolemy was born the Greek Eratosthenes computed the earth’s circumference from the angle of shadows cast by the sun, and derived a figure somewhat greater than Ptolemy’s. These “authorities” like d’Ailly have clearly been selected by the gentleman because their estimates of the earth’s figure all lie at the lower end of the range of accepted possibilities, the mean of which lies, I should judge, somewhere around four times bigger than that shown in the gentleman’s charts. And if that is so, if we were so foolish as to set off a boat into the western sea, the crew would never return - and nor would our money!’ That won a laugh.

But Harry knew he had a point, as he and Geoffrey had indeed selected many of the more helpful authorities and fed them to Colon.

Colon, however, was undeterred. He said simply that nobody could prove his figures right until the earth was sailed all the way around, but nobody could prove them wrong either.

He went on to the next leg of his case, that a voyage across the Ocean Sea would be no more than an extrapolation of journeys of exploration that had already been made - mostly by the Portuguese, he pointed out to the Spanish court. He spoke of developments in shipbuilding, and of the discovery of hitherto unknown islands in the Ocean Sea, from Madeira and the Canaries to the Azores.

And he spoke of earlier attempts to sail west across the Ocean Sea. He had collected many such tales in his years on Porto Santo and in Portugal. One Diogo de Tieve had sailed steadily south-west from the Azores, coming to a place where the condition of the sea and the circling of land birds indicated that land lay to the west, but he had had to return before it was reached. A Genoese merchant called Luca de Cazana had mounted several voyages that sailed west from the Azores for a hundred leagues or more, but in vain. Colon said that even unsuccessful explorations returned useful information about the state of the winds and the ocean currents. Colon himself had sailed far down the coast of Africa, and, he claimed, knew the Ocean Sea as well as any man alive.

Now he moved on to older legends. He referred to stories of the voyages of Saint Brendan and other Irish monks who had supposedly sailed far to the west across the north of the Ocean Sea, encountering mountains of ice and other strange phenomena. He quoted from the sagas of the Vikings, who, as was well known, had built churches in a western land so rich and warm that vines grew readily, so extensive it had never been explored properly.