"If you had the least doubt, monsieur le président--and I see that you have not--you would dig your cane, no great distance, twenty inches at most, into the sand beneath you. You would then encounter a resistance which would compel you to stop. That is the bags of gold. There ought to be eighteen hundred of them; and, as you see, they do not make an enormous heap. A kilogram of gold represents three thousand one hundred francs. Therefore, according to my calculation, a bag containing approximately fifty kilograms, or one hundred and fifty-five thousand francs done up in rouleaus of a thousand francs, is not a very large bag. Piled one against the other and one on top of the other, the bags represent a bulk of about fifteen cubic yards, no more. If you shape the mass roughly like a triangular pyramid you will have a base each of whose sides would be three yards long at most, or three yards and a half allowing for the space lost between the rouleaus of coins. The height will be that of the wall, nearly. Cover the whole with a layer of sand and you have the heap which lies before your eyes . . ." Don Luis paused once more before continuing: "And which has been there for months, monsieur le président, safe from discovery not only by those who were looking for it, but also by accident on the part of a casual passer-by. Just think, a heap of sand! Who would dream of digging a hole in it to see what is going on inside? The dogs sniff at it, the children play beside it and make mudpies, an occasional tramp lies down against it and takes a snooze. The rain softens it, the sun hardens it, the snow whitens it all over; but all this happens on the surface, in the part that shows. Inside reigns impenetrable mystery, darkness unexplored. There is not a hiding-place in the world to equal the inside of a sand heap exposed to view in a public place. The man who thought of using it to hide three hundred millions of gold, monsieur le président, knew what he was about." The late prime minister had listened to Don Luis' explanation without interrupting him. When Don Luis had finished, Valenglay nodded his head once or twice and said: "He did indeed. But there is one man who is cleverer still." "I don't believe it." "Yes, there's the man who guessed that the heap of sand concealed the three hundred million francs. That man is a master, before whom we must all bow." Flattered by the compliment, Don Luis raised his hat. Valenglay gave him his hand: "I can think of no reward worthy of the service which you have done the country." "I ask for no reward," said Don Luis. "I daresay, sir, but I should wish you at least to be thanked by voices that carry more weight than mine." "Is it really necessary, monsieur le président?" "I consider it essential. May I also confess that I am curious to learn how you discovered the secret? I should be glad, therefore, if you would call at my department in an hour's time."