Strabo, Geography
H.C. Hamilton, Esq., W. Falconer, M.A., Ed.

The countries beyond this which border upon the regions uninhabitable on account of their cold, have no interest to the geographer. He who desires to learn about them, and the celestial phenomena which Hipparchus has described, but which we pass over as being too much in detail for our present undertaking, must seek for them in that author. The statements of Posidonius concerning the periscii, the amphiscii, and the heteroscii are likewise too detailed. Still we must touch on these points sufficiently to explain his view, and to point out how far such matters are serviceable in geography, and how far not. The terms made use of refer to the shadows cast from the sun. The sun appears to the senses to describe a circle parallel to that of the earth.¹ Of those people for whom each revolution of the earth produces a day and a night, the sun being carried first over, then under, the earth, some are denominated amphiscii, others heteroscii. The amphiscii are the inhabitants of countries in which when a gnomon is placed perpendicularly on a plane surface, the shadow which it casts at mid-day, falls first to one side then to the other, as the sun illumines first this side, then that. This however only occurs in places situated between the tropics. The heteroscii are those amongst whom the shadow always falls to the north, as with us; or to the south, as amongst those who inhabit the other temperate zone. This occurs in all those regions where the arctic circle is less than the tropic. Where however it becomes the same as or greater than the tropic, this shows the commencement of the periscii, who extend thence to the pole. In regions where the sun remains above the horizon during an entire revolution of the earth, the shadow must evidently have turned in a complete circle round the gnomon. On this account he named them periscii. However they have nought to do with geography, inasmuch as the regions are not habitable on account of the cold, as we stated in our review of Pytheas. Nor is there any use in determining the size of this uninhabitable region, [it is enough to have established] that those countries, having the tropic for their arctic circle, are situated beneath the circle which is described by the pole of the zodiac² in the diurnal] revolution of the earth, and that the distance between the equator and the tropic equals four-sixtieths of the great circle [of the earth].