Genesis 41:31

The plenty shall not be known in the land by reason of that famine following - As Egypt depends for its fertility on the flowing of the Nile, and this flowing is not always equal, there must be a point to which it must rise to saturate the land sufficiently, in order to produce grain sufficient for the support of its inhabitants. Pliny, Hist. Nat., lib. v., cap. 9, has given us a scale by which the plenty and dearth may be ascertained; and, from what I have been able to collect from modern travelers, this scale may be yet considered as perfectly correct.

Justum incrementum est cubitorum 16. Minores aquae non omnia rigant, ampliores detinent, tardius recedendo. Hae serendi tempora absumunt, solo madente, Illae non dant, sitiente. Utrumque reputat provincia. In 12. cubitis famen sentit. In 13. etiamnum esurit; 14. cubita hilaritatem afferunt; 15. securitatem; 16. delicias.

"The ordinary height of the inundations is sixteen cubits. When the waters are lower than this standard they do not overflow the whole ground; when above this standard, they are too long in running off. In the first case the ground is not saturated: by the second, the waters are detained so long on the ground that seed-time is lost. The province marks both. If it rise only twelve cubits, a famine is the consequence. Even at thirteen cubits hunger prevails; fourteen cubits produces general rejoicing; fifteen, perfect security; and sixteen, all the luxuries of life."

When the Nile rises to eighteen cubits it prevents the sowing of the land in due season, and as necessarily produces a famine as when it does not overflow its banks.