As Dr. Draper has well pointed out (_Intellect. Develop. of Europe_, ed. 1875, i, 84-88), the peculiar regularity of Egyptian agriculture, depending as it did on the Nile overflow, which made known in advance the quantity of the crops, lent itself especially to a stable system of life and administration. The long-lasting exclusion of foreigners there, as in China and in Sparta, would further secure sameness of culture; and only by such causes can special unprogressiveness anywhere arise. Sir Henry Maine's formula, marking off progressive and unprogressive civilisations as different species, is merely verbal, and is not adhered to by himself. (The point is discussed at some length by the present writer in _Buckle and his Critics_, pp. 402-8.) Maine's distinction was drawn long ago by Eusèbe Salverte (_De la Civilisation depuis les premiers temps_, 1813, p. 22, _seq._), who philosophically goes on to indicate the conditions which set up the differentiation; though in later references (_Essai sur les noms d'hommes_, 1824, préf. p. ii; _Des Sciences occultes_, 1829, préf. p. vi) he recurs to the empirical form of his proposition, which is that adhered to by Maine. (4) When an old civilisation comes in steady contact with that of a race of not greatly inferior but less ancient culture, physically so situated as to be much less amenable to despotism (that is, in a hilly or otherwise easily defensible region), it is likely so to fecundate the fresher civilisation that the latter, if not vitiated by a bad political system, will soon surpass it,[135] provided that the latter community in turn is duly crossed as regards its stock, and that the former has due resources. (5) In other words, a primitive but not barbarous people, placed in a region not highly fruitful but not really unpropitious to human life, is the less likely to fall tamely under a despotism because its population is not so easily multiplied and maintained;[136] and such a people, when physiologically variated by a mixture of stocks, and when mentally fecundated by contact with older civilisations, tends to develop what we term a secondary civilisation, higher in all respects than those which have stimulated it.[137] (6) A very great disparity in the culture-stages of meeting races, however, is as unfavourable to the issue of a higher civilisation from their union as to a useful blending of their stocks.[138] Thus it fares ill with the contact of higher and lower races even in a climate equally favourable to both; and where it is favourable to the latter only, there is likely to be no immediate progress in the lower race, while in the terms of the case the higher will deteriorate or disappear.[139]