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greatest is not comparable in size with any one of the arms of the Nile." After comparing the valley of the Nile with that of the Red Sea (which Herodotus appears not to have visited, and of the magnitude of which he has a very inadequate conception), he goes on to say: "Now, if the Nile should choose to divert his waters from their present bed into the Arabian Gulf, what is to prevent it from being filled up by the stream within twenty thousand years at most? For my part, I think it might be filled up in half the time. Why, then, should not a gulf of even much larger size have been filled up in the ages before I was born, by a river which is so large and so given to working changes as the Nile?"

It is on the strength of these very sound and just physical considerations that Herodotus tells us he accepted Egyptian tradition:

"Thus I gave credit to those from whom I received this account of Egypt, and am myself, moreover, strongly of the same opinion, since I remarked that the country projects into the sea farther than the surrounding shores, and I observed that there were shells upon the hills." Finally, he inquires into the origin of the population of Egypt:

"I do not believe that the Egyptians came into being at the same time as the delta. I think they have always existed, ever since the human race began. As the land went on increasing, part of the population came down into the new country, part remained in the old settlements."

Thus Herodotus commits himself to four very definite propositions respecting the unwritten history of Egypt:

1. That the delta was once an arm of the sea.

2. That it has been filled up and converted into dry land by the alluvial deposits of the Nile.

3. That this process of conversion into dry land probably took something like twenty thousand years.

4. That the Egyptians existed before Lower Egypt, and migrated thence from Upper Egypt.

And it will be observed that the first three of these propositions at any rate are not mere guesses, but conclusions based upon a process of reasoning from analogy, just as sound in form as any which is to be met with in the discussion of a similar problem in a modern treatise on geology.

Herodotus wrote twenty-three hundred years ago. In the course of twenty-one out of the twenty-three centuries which have elapsed since his time, I am not aware that any one rose above his level in the discussion of such problems as that which he attacked. And some quite modern writers have not yet reached it, for lack of as much knowledge of natural phenomena as Herodotus possessed. Let us look at the facts by the light of such knowledge of elementary physical science as is now happily accessible to every Etonian.