“Further still, as the elements are solids, how can they be bound together through one medium? For this is impossible in solids, as we have before observed. Hence those who assert these things, neither speak mathematically nor physically, but unavoidably err in both these respects. For physical are derived from mathematical entities. _Timæus therefore alone, or any other who rightly follows him, neither attributes one or two powers alone to the elements, but triple powers; to fire indeed tenuity of parts, acuteness, and facility of motion; to air, tenuity of parts, obtuseness, and facility of motion; to water, grossness of parts, obtuseness, and facility of motion; and to earth, grossness of parts, obtuseness, and difficulty of motion._ But this is in order that each of the elements may have two powers, each[28] of which is common to the element placed next to it, and one power which is different, in the same manner as it was demonstrated in mathematical numbers and figures; this different power being assumed from one of the extremes; and also in order that earth, according to all the powers, may subsist oppositely to fire; and that the extremes may have two media, and the continued quantities two; the latter having solids for the media, but the former, common powers. For let fire indeed be attenuated in its parts, acute, and easily moved. For it has an attenuated essence, and is acute, as having a figure of this kind [i. e. a pyramidal figure], and on this account is incisive and fugitive[29], and permeates through all the other elements. It is also moved with facility[30], as being most near to the celestial bodies, and existing in them. For the celestial fire itself is moved with celerity, as is likewise sublunary fire, which is perpetually moved in conjunction with it, and according to one circle, and one impulse. Since, therefore, earth is contrary to fire, it has contrary powers, viz. grossness, obtuseness, and difficulty of motion, all which we see are present with it. But these being thus hostile, and being solids, are also similar solids. For their sides and their powers are analogous. For as the gross is to the attenuated, so is the obtuse to the acute, and that which is moved with difficulty, to that which is moved with facility. But those are similar solids of which the sides that constitute the bodies are analogous. _For the sides are the powers of which bodies consist._ Hence, as fire and earth are similar bodies, and similar solids, two analogous media fall between them; and each of the media will have two sides of the extremes situated next to it, and the remaining side from the other extreme. Hence, since fire has for its three physical sides the triple powers, tenuity, acuteness, and facility of motion, by taking away the middle power, acuteness, and introducing instead of it obtuseness, we shall produce air, which has two sides of fire, but one of earth, or two