distant, tend to its centre, and that every body is attracted
towards its centre by gravity. This is more distinctly proved
from observations of the sea and sky, for here the evidence of
the senses and common observation is alone requisite. The
convexity of the sea is a further proof of this to those who have
sailed, for they cannot perceive lights at a distance when placed
at the same level as their eyes, and if raised on high they at
once become perceptible to vision though at the same time farther
removed. So when the eye is raised it sees what before was
utterly imperceptible. Homer speaks of this when he says:


" 'Lifted up on the vast wave he quickly beheld afar.'

Sailors as they approach their destination behold the shore
continually raising itself to their view, and objects which had
at first seemed low begin to lift themselves. Our gnomons, also,
are, among other things, evidence of the revolution of the
heavenly bodies, and common-sense at once shows us that if the
depth of the earth were infinite such a revolution could not take
place."[1]

Elsewhere Strabo criticises Eratosthenes for having entered into
a long discussion as to the form of the earth. This matter,
Strabo thinks, "should have been disposed of in the compass of a
few words." Obviously this doctrine of the globe's sphericity
had, in the course of 600 years, become so firmly established
among the Greek thinkers as to seem almost axiomatic. We shall
see later on how the Western world made a curious recession from
this seemingly secure position under stimulus of an Oriental
misconception. As to the size of the globe, Strabo is disposed to
accept without particular comment the measurements of
Eratosthenes. He speaks, however, of "more recent measurements,"
referring in particular to that adopted by Posidonius, according
to which the circumference is only about one hundred and eighty
thousand stadia. Posidonius, we may note in passing, was a
contemporary and friend of Cicero, and hence lived shortly before
the time of Strabo. His measurement of the earth was based on
observations of a star which barely rose above the southern
horizon at Rhodes as compared with the height of the same star
when observed at Alexandria. This measurement of Posidonius,
together with the even more famous measurement of Eratosthenes,
appears to have been practically the sole guide as to the size of
the earth throughout the later periods of antiquity, and, indeed,
until the later Middle Ages.

As becomes a writer who is primarily geographer and historian
rather than astronomer, Strabo shows a much keener interest in
the habitable portions of the globe than in the globe as a whole.
He assures us that this habitable portion of the earth is a great
island, "since wherever men have approached the termination of
the land, the sea, which we designate ocean, has been met with,
and reason assures us of the similarity of this place which our
senses have not been tempted to survey." He points out that
whereas sailors have not circumnavigated the globe, that they had
not been prevented from doing so by any continent, and it seems
to him altogether unlikely that the Atlantic Ocean is divided
into two seas by narrow isthmuses so placed as to prevent
circumnavigation. "How much more probable that it is confluent
and uninterrupted. This theory," he adds, "goes better with the
ebb and flow of the ocean. Moreover (and here his reasoning
becomes more fanciful), the greater the amount of moisture
surrounding the earth, the easier would the heavenly bodies be
supplied with vapor from thence." Yet he is disposed to believe,
following Plato, that the tradition "concerning the island of
Atlantos might be received as something more than idle fiction,
it having been related by Solon, on the authority of the Egyptian
priests, that this island, almost as large as a continent, was
formerly in existence although now it had disappeared."[2]

In a word, then, Strabo entertains no doubt whatever that it
would be possible to sail around the globe from Spain to India.
Indeed, so matter-of-fact an inference was this that the feat of
Columbus would have seemed less surprising in the first century
of our era than it did when actually performed in the fifteenth
century. The terrors of the great ocean held the mariner back,
rather than any doubt as to where he would arrive at the end of
the voyage.

Coupled with the idea that the habitable portion of the earth is
an island, there was linked a tolerably definite notion as to the
shape of this island. This shape Strabo likens to a military
cloak. The comparison does not seem peculiarly apt when we are
told presently that the length of the habitable earth is more
than twice its breadth. This idea, Strabo assures us, accords
with the most accurate observations "both ancient and modern."
These observations seemed to show that it is not possible to live
in the region close to the equator, and that, on the other hand,
the cold temperature sharply limits the habitability of the globe
towards the north. All the civilization of antiquity clustered
about the Mediterranean, or extended off towards the east at
about the same latitude. Hence geographers came to think of the
habitable globe as having the somewhat lenticular shape which a
crude map of these regions suggests. We have already had occasion
to see that at an earlier day Anaxagoras was perhaps influenced
in his conception of the shape of the earth by this idea, and the
constant references of Strabo impress upon us the thought that
this long, relatively narrow area of the earth's surface is the
only one which can be conceived of as habitable.



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