The lesser problem immediately absorbed Bony. Why did the ants bring up out of the nest one stone and take another down? And whence had they collected the small smooth stones in all that great expanse of sand, fine almost as a speck of whirling dust in a sunbeam?

The ants worked on, unheeding him. They all appeared possessed of but one idea. There came to Bony memory of reading of the punishments meted out to prisoners in the old convict days, when a man was compelled to carry a heavy shot up an incline, there to let it roll back, then to return and again carry it up.

But that was all insensate stupidity and cruelty. There is certainly no stupidity of that order among ants. They were not carrying stones up and down for mere exercise, and they were not so developed as to impose such work as a punishment.

“Bony, you read too much,” he said aloud. “You read so much that you forget ninety per cent of what you have read. Somewhere, some time, you’ve read about ants carrying stones.” For many minutes he sat, leaning back on his elbow, his mind’s eye so active that his physical eyes were without vision. Almost fifteen minutes expired before he sighed with satisfaction. He had remembered. The ants were taking down sun-heated stones to keep the eggs warm, and were bringing up cold stones to be heated by the early rays of the sun when next it rose. “That’s it!” he murmured. “They do nothing without a logical cause. Ah! Why, here comes one with a piece of blue glass. Evidently glass does not retain heat as rock will. I must inquire into that.”

Up out of thehole an ant carried a piece of blue glass, which reflected the light strongly whilst it was still deep in the shadow. The insect brought it up to the west slope of the rampart and laid it there before hurrying round for a sun-warmed stone. Bony picked it up with the point of his knife and examined it closely on the palm of his hand.