the earth's roundness; St. Isidore taught it; and so also did St.
Augustine, as we might expect from a man of his wisdom who lived so long
in a monastery that looked out to sea from a high point, and who wrote
the words 'Ubi magnitudo, ibi veritas'. In the sixth century of the
Christian era Bishop Cosmas gave much thought to this matter of a round
world, and found a new argument which to his mind (poor Cosmas!) disposed
of it very clearly; for he argued that, if the world were round, the
people dwelling at the antipodes could not see Christ at His coming, and
that therefore the earth was not round. But Bede, in the eighth century,
established it finally as a part of human knowledge that the earth and
all the heavenly bodies were spheres, and after that the fact was not
again seriously disputed.

What lay beyond the frontier of the known was a speculation inseparable
from the spirit of exploration. Children, and people who do not travel,
are generally content, when their thoughts stray beyond the paths trodden
by their feet, to believe that the greater world is but a continuation on
every side of their own environment; indeed, without the help of sight or
suggestion, it is almost impossible to believe anything else. If you
stand on an eminence in a great plain and think of the unseen country
that lies beyond the horizon, trying to visualise it and imagine that you
see it, the eye of imagination can only see the continuance or projection
of what is seen by the bodily sight. If you think, you can occupy the
invisible space with a landscape made up from your own memory and
knowledge: you may think of mountain chains and rivers, although there
are none visible to your sight, or you may imagine vast seas and islands,
oceans and continents. This, however, is thought, not pure imagination;
and even so, with every advantage of thought and knowledge, you will not
be able to imagine beyond your horizon a space of sea so wide that the
farther shore is invisible, and yet imagine the farther shore also. You