Now it ought to be obvious that this is no innovation. Of course the employment of the letter alpha to represent the units is derived from the conventional notation; but otherwise we are clearly in presence of something which belongs to the very earliest stage of the science. We also gather that the dots were supposed to represent pebbles (ψῆφοι), and this throws light on early methods of what we still call calculation.
48.Triangular, square and oblong numbers. That Aristotle refers to this seems clear, and is confirmed by the tradition that the great revelation made by Pythagoras to mankind was precisely a figure of this kind, the tetraktys, by which the Pythagoreans used to swear,[1] and we have the authority of Speusippos for holding that the whole theory was Pythagorean.[2] In later days there were many kinds of tetraktys,[3] but the original one, that by which the Pythagoreans swore, was the "tetraktys of the dekad." It was a figure like this:
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and represented the number ten as the triangle of four.
- ↑ Cf. the formula Οὐ μὰ τὸν ἁμετέρᾳ γενεᾷ παραδόντα τετρακτύν, which is all the more likely to be old that it is put into the mouth of Pythagoras by the forger of the Χρυσᾶ ἔπη, thus making him swear by himself ! See Diels, Arch. iii. p. 457.
- ↑ Speusippos wrote a work on the Pythagorean numbers, based chiefly on Philolaos, and a considerable fragment of it is preserved in the Theologumena Arithmetica. It will be found in Diels, Vorsokratiker, 32 A 13, and is discussed by Tannery, Science hellène, pp. 374 sqq.
- ↑ See Theon, Expositio, pp. 93 sqq., Hiller. The τετρακτύς used in the Timaeus is the second described by Theon (Exp. p. 94, 10 sqq.).
δὲ διάστασιν προβήσεται ὁ τοιοῦτος, διὰ τοῦτο δὲ αὐτὸν καὶ εὐθυμετρικόν τινες καλοῦσι, Θυμαρίδας δὲ καὶ εὐθυγραμμικόν· ἀπλατὴς γὰρ ἐν τῇ ἐκθέσει ἐφ' ἓν μόνον διιστάμενος. It is generally recognised now that Thymaridas was an early Pythagorean (Tannery, Mém. scient. vol. i. n. 9; G. Loria, Scienze esatte, p. 807); and, if that is so, we have a complete proof that this theory goes back to the early days of the school. For the triangular, oblong, and square numbers, etc., see Theon of Smyrna, pp. 27-37, Hiller, and Nicom. loc. cit.
