The explanation given in the text supposes the two harmonies to make up the number 8000. This explanation derives a certain plausibility from the circumstance that 8000 is the ancient number of the Spartan citizens (Herod.), and would be what Plato might have called ‘a number which nearly concerns the population of a city’; the mysterious disappearance of the Spartan population may possibly have suggested to him the first cause of his decline of States. The lesser or square ‘harmony,’ of 400, might be a symbol of the guardians,—the larger or oblong ‘harmony,’ of the people, and the numbers 3, 4, 5 might refer respectively to the three orders in the State or parts of the soul, the four virtues, the five forms of government. The harmony of the musical scale, which is elsewhere used as a symbol of the harmony of the state, is also indicated. For the numbers 3, 4, 5, which represent the sides of the Pythagorean triangle, also denote the intervals of the scale. The terms used in the statement of the problem may be explained as follows. A perfect number (Greek), as already stated, is one which is equal to the sum of its divisors. Thus 6, which is the first perfect or cyclical number, = 1 + 2 + 3. The words (Greek), ‘terms’ or ‘notes,’ and (Greek), ‘intervals,’ are applicable to music as well as to number and figure. (Greek) is the ‘base’ on which the whole calculation depends, or the ‘lowest term’ from which it can be worked out. The words (Greek) have been variously translated—‘squared and cubed’ (Donaldson), ‘equalling and equalled in power’ (Weber), ‘by involution and evolution,’ i.e. by raising the power and extracting the root (as in the translation). Numbers are called ‘like and unlike’ (Greek) when the factors or the sides of the planes and cubes which they represent are or are not in the same ratio: e.g. 8 and 27 = 2 cubed and 3 cubed; and conversely. ‘Waxing’ (Greek) numbers, called also ‘increasing’ (Greek), are those which are exceeded by the sum of their divisors: e.g. 12 and 18 are less than 16 and 21. ‘Waning’ (Greek) numbers, called also ‘decreasing’ (Greek) are those which succeed the sum of their divisors: e.g. 8 and 27 exceed 7 and 13. The words translated ‘commensurable and agreeable to one another’ (Greek) seem to be different ways of describing the same relation, with more or less precision. They are equivalent to ‘expressible in terms having the same relation to one another,’ like the series 8, 12, 18, 27, each of which numbers is in the relation of (1 and 1/2) to the preceding. The ‘base,’ or ‘fundamental number, which has 1/3 added to it’ (1 and 1/3) = 4/3 or a musical fourth. (Greek) is a ‘proportion’ of numbers as of musical notes, applied either to the parts or factors of a single number or to the relation of one number to another. The first harmony is a ‘square’ number (Greek); the second harmony is an ‘oblong’ number (Greek), i.e. a number representing a figure of which the opposite sides only are equal.