Some years passed before I had an opportunity of talking to Lupin about this business. He was in a confidential vein and answered: "The business of the eighteen diamonds? By Jove, when I think that three or four generations of my fellow-men had been hunting for the solution! And the eighteen diamonds were there all the time, under a little mud and dust!" "But how did you guess?..." "I did not guess. I reflected. I doubt if I need even have reflected. I was struck, from the beginning, by the fact that the whole circumstance was governed by one primary question: the question of time. When Charles d'Ernemont was still in possession of his wits, he wrote a date upon the three pictures. Later, in the gloom in which he was struggling, a faint glimmer of intelligence led him every year to the centre of the old garden; and the same faint glimmer led him away from it every year at the same moment, that is to say, at twenty-seven minutes past five. Something must have acted on the disordered machinery of his brain in this way. What was the superior force that controlled the poor madman's movements? Obviously, the instinctive notion of time represented by the sun-dial in the farmer-general's pictures. It was the annual revolution of the earth around the sun that brought Charles d'Ernemont back to the garden at a fixed date. And it was the earth's daily revolution upon its own axis that took him from it at a fixed hour, that is to say, at the hour, most likely, when the sun, concealed by objects different from those of to-day, ceased to light the Passy garden. Now of all this the sun-dial was the symbol. And that is why I at once knew where to look." "But how did you settle the hour at which to begin looking?" "Simply by the pictures. A man living at that time, such as Charles d'Ernemont, would have written either 26 Germinal, Year II, or else 15 April, 1794, but not 15 April, Year II. I was astounded that no one had thought of that." "Then the figure 2 stood for two o'clock?" "Evidently. And what must have happened was this: the farmer-general began by turning his fortune into solid gold and silver money. Then, by way of additional precaution, with this gold and silver he bought eighteen wonderful diamonds. When he was surprised by the arrival of the patrol, he fled into his garden. Which was the best place to hide the diamonds? Chance caused his eyes to light upon the sun-dial. It was two o'clock. The shadow of the arrow was then falling along the crack in the marble. He obeyed this sign of the shadow, rammed his eighteen diamonds into the dust and calmly went back and surrendered to the soldiers." "But the shadow of the arrow coincides with the crack in the marble every day of the year and not only on the 15th of April." "You forget, my dear chap, that we are dealing with a lunatic and that he remembered only this date of the 15th of April."