The number of zones accepted by Strabo is five, and he criticises Polybius for making the number six. The five zones accepted by Strabo are as follows: the uninhabitable torrid
zone lying in the region of the equator; a zone on either side of this extending to the tropic; and then the temperate zones extending in either direction from the tropic to the arctic regions. There seems to have been a good deal of dispute among the scholars of the time as to the exact arrangement of these zones, but the general idea that the north-temperate zone is the part of the earth with which the geographer deals seemed clearly established. That the south-temperate zone would also present a habitable area is an idea that is sometimes suggested, though seldom or never distinctly expressed. It is probable that different opinions were held as to this, and no direct evidence being available, a cautiously scientific geographer like Strabo would naturally avoid the expression of an opinion regarding it.
Indeed, his own words leave us somewhat in doubt as to the precise character of his notion regarding the zones. Perhaps we shall do best to quote them:
“Let the earth be supposed to consist of five zones. (1) The equatorial circle described around it. (2) Another parallel to this, and defining the frigid zone of the northern hemisphere.
(3) A circle passing through the poles and cutting the two preceding circles at right- angles. The northern hemisphere contains two quarters of the earth, which are bounded by the equator and circle passing through the poles. Each of these quarters should be supposed to contain a four-sided district, its northern side being of one-half of the parallel next the pole, its southern by the half of the equator, and its remaining sides by two segments of the circle drawn through the poles, opposite to each other, and equal in length. In one of these (which of them is of no consequence) the earth which we inhabit is situated, surrounded by a sea and similar to an island. This, as we said before, is evident both to our senses and to our reason.
But let any one doubt this, it makes no difference so far as geography is concerned whether you believe the portion of the earth which we inhabit to be an island or only admit what we know from experience –namely, that whether you start from the east or the west you may sail all around it. Certain intermediate spaces may have been left (unexplored), but these are as likely to be occupied by sea as uninhabited land. The object of the geographer is to describe known countries. Those which are unknown he passes over equally with those beyond the limits of the inhabited earth.
It will, therefore, be sufficient for describing the contour of the island we have been speaking of, if we join by a right line the outmost points which, up to this time, have been explored by voyagers along the coast on either side.”[3]
We may pass over the specific criticisms of Strabo upon various explorations that seem to have been of great interest to his contemporaries, including an alleged trip of one Eudoxus out into the Atlantic, and the journeyings of Pytheas in the far north. It is Pytheas, we may add, who was cited by Hipparchus as having made the mistaken observation that the length of the shadow of the gnomon is the same at Marseilles and Byzantium, hence that these two places are on the same parallel. Modern commentators have defended Pytheas as regards this observation, claiming that it was Hipparchus and not Pytheas who made the second observation from which the faulty induction was drawn. The point is of no
great significance, however, except as showing that a correct method of determining the problems of latitude had thus early been suggested. That faulty observations and faulty application of the correct principle should have been made is not surprising.
Neither need we concern ourselves with the details as to the geographical distances, which Strabo found so worthy of criticism and controversy. But in leaving the great geographer we may emphasize his point of view and that of his contemporaries by quoting three fundamental principles which he reiterates as being among the “facts established by natural philosophers.” He tells us that “(1) The earth and heavens are spheroidal. (2) The tendency of all bodies having weight is towards a centre. (3) Further, the earth being spheroidal and having the same centre as the heavens, is motionless, as well as the axis that passes through both it and the heavens. The heavens turn round both the earth and its axis, from east to west. The fixed stars turn round with it at the same rate as the whole. These fixed stars follow in their course parallel circles, the principal of which are the equator, two tropics, and the arctic circles; while the planets, the sun, and the moon describe certain circles comprehended within the zodiac.”[4]