Instead of flying back to the pyramid for the last load, Arcot announced that he was going to leave a note for anyone who might come here later. While the others went back for the last load, he worked at drawing the "note". "Let's see your masterpiece," said Morey as the three men returned to the ship with the last of the books. Arcot had used a piece of tough, heavy plastic which would resist any corrosion the cold, almost airless world might have to offer. Near the top, he had drawn a representation of their ship, and beneath it a representation of the route they had taken from universe to universe. The galaxy they were in was represented by a cloud of gas, its main identifying feature. Underneath the dotted line of their route through space, he had printed "200,000,000,000, _u_". Then followed a little table. The numeral "1" followed by a straight bar, then "2" followed by two bars, and so on up to ten. Ten was represented by ten bars and, in addition, an S-shaped sign. Twenty was next, followed by twenty bars and two S-shaped signs. Thus he had worked up to "100". The system he used would make it clear to any reasoning creature that he had used a decimal system and that the zeroes meant ten times. Next below, he had drawn the planetary system of the frozen world, and the distance from the planet they were on to the central sun he labeled "_u_". Thus, the finders could reason that they had come a distance of two hundred billion units, where a distance of three hundred million miles was taken as the unit; they had, then, come from another galaxy. Certainly any creature with enough intelligence to reach this frozen world would understand this! "Since the year of this planet is approximately eight times our own," Arcot continued, "I am indicating that we came here approximately five hundred years after the catastrophe." He pointed at several of the other drawings. They left the message in the tower, and Arcot closed the door, leaving the pyramid exactly as it had been before they had come. "Say!" Morey commented, "how did you open and close that door, anyway?" Arcot grinned. "Didn't you notice the jewel at the corner? It was the lens of a photoelectric cell. My flashlight opened the door. I didn't figure it out; it just worked accidentally." Morey raised an eyebrow. "But if the darned thing is so simple, any creature, intelligent or not, might be able to get in and destroy the records!" Arcot looked at him. "And where are your savages going to come from? There are none on this planet, and anyone intelligent enough to build a spaceship isn't going to destroy the contents of the tower." "Oh." Morey looked a little sheepish. They went into the airlock and took off their suits. Then they began packing the precious books in specimen cases that had been brought for the purpose of preserving such things.