"Do you think it was simply an echo?"
"Undoubtedly; didn't you hear Baby's cries repeated?"
"But how do you know that the hills are 2,000 feet away?"
"Sound travels at the rate of 1,040 feet per second, and I made a mental calculation that it took four seconds for Baby's cries to come back from the hills. In that case the sound had to go to the hills and back again, and it would, therefore, take two seconds to travel one way. Do you understand?"
"Oh, yes; that is perfectly clear."
The land now became more rolling, and was occasionally broken by ravines; and sometimes they had difficulty in getting their yaks and wagon across and over the rough ground.
Fallen trees were numerous; there were little mounds here and there, made by the remains of uprooted trees, which had long ago decayed, all of which made their traveling laborious and slow.
Here wild animals became more abundant, and wild game was found on every side. Several good shots by the boys replenished their larder with bird meat.
"See that bear!" cried Harry in great excitement.
The boys, as well as the Professor, were out with their guns at once. "Follow him up quickly now," and the Professor could hardly keep pace with them. The bear did not seem to be greatly frightened, and when Harry, who was ahead, stopped and aimed his gun for a shot, he was less than a hundred feet away. The shots from the two boys came close together, and bruin stopped in surprise, then, with a snarl, turned around and in a lumbering, shuffling movement started for the boys.