A sudden thought came to Jerry. He whispered to the professor.
“Of course it could be done,” replied the scientist after consideration, “but there is the danger of the water rising suddenly while we are in the tunnel. Jerry talks of escaping by means of this new shaft,” went on the professor. “We could run the auto down the incline and so out. But we must investigate the place.”
The naturalist walked down the incline. Straight in front of them, as they neared it, yawned the black mouth of the passage. The professor would not let the boys come in until he had made an investigation.
He walked quite a distance down the shaft and returned. He seemed in deep thought.
“It will be safe to use the tunnel,” he said. “It appears that the water was siphoned out. There is another tank or reservoir connected with this one. They both seem to be fed by springs. When the other tank, which is below the level and to one side, gets full of water, the fluid is siphoned out. As that tank is connected with the one we used, by a pipe, as soon as the water goes out of the first tank, that in the second follows to keep the first tank filled. And so it goes on, from day to day, repeating the operation once every twenty-four hours, I would judge. So we have plenty of time. The tunnel leads to one like that by which we entered the city. I have no doubt but that we can escape through it.”
If the professor and the boys could at this time have seen two evil faces peering down at them from a high balcony, they might not have felt so comfortable. San Lucia and Murado were on the lookout, and every move the travelers made was watched.
It was decided to make the escape that night. Accordingly, after supper, the automobile was prepared for a long trip. Things were packed in it, and the professor took along his beloved specimens.
“How are we going to get the car down the incline?” asked Bob.
“I can take it down, all right,” replied Jerry.
At length all was in readiness. Jerry and Ned took the front seat, Bob cranked up the car, which was still inside the old temple, and then joined the professor on the rear seat.