27. The air that Anaximenes speaks of includes a good deal that we should not call by that name. In its normal condition, when most evenly distributed, it is invisible, and it then corresponds to our “air”; it is identical with the breath we inhale and the wind that blows. That is why he called it πνεῦμα. On the other hand, the old idea, familiar to us in Homer, that mist or vapour is condensed air, is still accepted without question. In other words, we may say that Anaximenes supposed it to be a good deal easier to get liquid air than it has since proved to be. It was Empedokles, we shall see, who first discovered that what we call air was a distinct corporeal substance, and was not identical either with vapour or with empty space. In the earlier cosmologists “air” is always a form of vapour, and even darkness is a form of it. It was Empedokles who cleared up this point too by showing that darkness is a shadow.[154] Footnote 154: For the meaning of ἀήρ in Homer, see Schmidt, _Synonomik_, § 35; and for its survival in Ionic prose, Hippokrates, Περὶ ἀέρων, ὑδάτων, τόπων, 15, ἀήρ τε πολὺς κατέχει τὴν χώρην ἀπὸ τῶν ὑδάτων. Plato is still conscious of the old meaning of the word; for he makes Timaios say ἀέρος (γένη) τὸ μὲν εὐαγέστατον ἐπίκλην αἰθὴρ καλούμενος, ὁ δὲ θολερώτατος ὁμίχλη καὶ σκότος (_Tim._ 58 d). The view given in the text has been criticised by Tannery, “Une nouvelle hypothèse sur Anaximandre” (_Arch._ viii. pp. 443 sqq.), and I have slightly altered my expression of it to meet these criticisms. The point is of fundamental importance, as we shall see, for the interpretation of Pythagoreanism. It was natural for Anaximenes to fix upon Air in this sense as the primary substance; for, in the system of Anaximander, it occupied an intermediate place between the two fundamental opposites, the sphere of flame and the cold, moist mass within it (§ 19). We know from Plutarch that he fancied air became warmer when rarefied, and colder when condensed. Of this he satisfied himself by a curious experimental proof. When we breathe with our mouths open, the air is warm; when we breathe with our lips closed, it is cold.[155] Footnote 155: Plut. _de prim. frig._ 947 f (R. P. 27). [Sidenote: The world breathes.] 28. This argument from human breathing brings us to an important point in the theory of Anaximenes, which is attested by the single fragment that has come down to us.[156] “Just as our soul, being air, holds us together, so do breath and air encompass the whole world.” The primary substance bears the same relation to the life of the world as to that of man. Now this, we shall see, was the Pythagorean view;[157] and it is also an early instance of the argument from the microcosm to the macrocosm, and so marks the first beginnings of an interest in physiological matters. Footnote 156: Aet. i. 3, 4 (R. P. 24). Footnote 157: See Chap. II. § 53. [Sidenote: The parts of the world.]