The instrument stood upon a low stone pedestal. It consisted of a transparent cylinder about twelve inches in diameter and some four feet high, surmounted by a large circular bowl. The cylinder was separated from the bowl by a broad disc of porous stone; a similar stone section divided the cylinder horizontally into halves. From the bowl a fluid was dropping in a tiny stream through the top stone segment into the upper compartment, which was now about half full. This in turn filtered through the second stone into the lower compartment. This lower section was marked in front with a large number of fine horizontal lines, an equal distance apart, but of unequal length. In it the fluid stood now just above one of the longer lines-the fourth from the bottom. On the top of this fluid floated a circular disc almost the size of the inside diameter of the cylinder. The Chemist explained. "It really is very much like the old hour-glass we used to have in your world. This filters liquid instead of sand. You will notice the water filters twice." He indicated the two compartments. "That is because it is necessary to have a liquid that is absolutely pure in order that the rate at which it filters through this other stone may remain constant. The clock is carefully tested, so that for each eclipse the water will rise in this lower part of the cylinder, just the distance from here to here." The Chemist put his fingers on two of the longer marks. "Very ingenious," remarked the Doctor. "Is it accurate?" "Not so accurate as your watches, of course," the Chemist answered. "But still, it serves the purpose. These ten longer lines, you see, mark the ten eclipses that constitute one of our days. The shorter lines between indicate halves and quarter intervals." "Then it is only good for one day?" asked the Very Young Man. "How do you set it?" "It resets automatically each day, at the beginning of the first eclipse. This disc," the Chemist pointed to the disc floating on the water in the lower compartment. "This disc rises with the water on which it is floating. When it reaches the top of it, it comes in contact with a simple mechanism--you'll see it up there--which opens a gate below and drains out the water in a moment. So that every morning it is emptied and starts filling up again. All that is needed is to keep this bowl full of water." "It certainly seems very practical," observed the Big Business Man. "Are there many in use?" "Quite a number, yes. This clock was invented by Reoh, some thirty years ago. He is the greatest scientist and scholar we have." The old man smiled deprecatingly at this compliment. "Are these books?" asked the Very Young Man; he had wandered over to the table and was fingering one of the bound sheets of parchment. "They are Reoh's chronicles," the Chemist answered. "The only ones of their kind in Arite." "What's this?" The Very Young Man pointed to another instrument.