If of the more recent measurements we prefer those which diminish the size of the earth, such as that adopted by Posidonius, which is about 180,000 stadia,[628] the torrid zone will still only occupy half, or rather more than half, of the space comprised between the tropics; but never an equal space. [Respecting the system of Aristotle, Posidonius farther says,] “Since it is not every latitude which has Arctic Circles,[629] and even those which do possess them have not the same, how can any one determine by them the bounds of the temperate zones, which are immutable?” Nothing however is proved [against Aristotle] from the fact that there are not Arctic Circles for every latitude, since they exist for all the inhabitants of the temperate zone, on whose account alone the zone receives its name of temperate. But the objection that the Arctic Circles do not remain the same for every latitude, but shift their places, is excellent.[630] 3. Posidonius, who himself divides the earth into zones, tells us that “five is the number best suited for the explanation of the celestial appearances, two of these are periscii,[631] which reach from the poles to the point where the tropics serve for Arctic Circles; two more are heteroscii,[632] which extend from the former to the inhabitants of the tropics, and one between the tropics, which is called amphiscius,[633] but for matters relative to the earth, it is convenient to suppose two other narrow zones placed under the tropics, and divided by them into two halves, over which [every year] for the space of a fortnight, the sun is vertical.”[634] These zones are remarkable for being extremely arid and sandy, producing no vegetation with the exception of silphium,[635] and a parched grain somewhat resembling wheat. This is caused by there being no mountains to attract the clouds and produce rain, nor any rivers flowing[636] through the country. The consequence is that the various species[637] are born with woolly hair, crumpled horns, protruding lips, and wide nostrils; their extremities being as it were gnarled. Within these zones also dwell the Ichthyophagi.[638] He further remarks, that these peculiarities are quite sufficient to distinguish the zones in question: those which are farther south having a more salubrious atmosphere, and being more fruitful and better supplied with water. CHAPTER III.