oger
Pietro d' Abano, in his book _Conciliator Differentiarum_,
written about 1312. (See Major, _Prince Henry the Navigator_,
p. 100.) It plays an important part in one of the finest tales
in the _Arabian Nights_,--the story of the "Third Royal
Mendicant."]

[Sidenote: Going downhill.]

Besides this dread of the burning zone, another fanciful obstacle beset
the mariner who proposed to undertake a long voyage upon the outer
ocean. It had been observed that a ship which disappears in the offing
seems to be going downhill; and many people feared that if they should
happen thus to descend too far away from the land they could never get
back again. Men accustomed to inland sea travel did not feel this dread
within the regions of which they had experience, but it assailed them
whenever they thought of braving the mighty waters outside.[369] Thus
the master mariner, in the Middle Ages, might contemplate the possible
chance of being drawn by force of gravity into the fiery gulf, should he
rashly approach too near; and in such misgivings he would be confirmed
by Virgil, who was as much read then as he is to-day and esteemed an
authority, withal, on scientific questions; for according to Virgil the
Inhabited World descends toward the equator and has its apex in the
extreme north.[370]

[Footnote 369: Ferdinand Columbus tells us that this objection
was urged against the Portuguese captains and afterwards
against his father: "E altri di cio quasi cosi disputavano,
come gia i Portoghesi intorno al navigare in Guinea; dicendo
che, se si allargasse alcuno a far cammino diritto al
occidente, come l' Ammiraglio diceva, non potrebbe poi tornare
in Ispagna per la rotondita della sfera; tenendo per
certissime, che qualunque uscisse del emisperio conosciuto da
Tolomeo, anderebbe in giu, e poi gli sarebbe impossibile dar la
volta; e affermando che cio sarebbe quasi uno ascendere all'
insu di un monte. Il che non potrebbono fare i navigli con
grandissimo vento." _Vita deli' Ammiraglio_, Venice, 1571, cap.
xii. The same thing is told, in almost the same words, by Las
Casas, since both writers followed the same original documents:
"Anidian mas, que quien navegase por via derecha la vuelta del
poniente, como el Cristobal Colon proferia, no podria despues