CHAPTER VII
CAUGHT IN THE DEEP SEA NETS
The starting of the heavy machinery was sufficient indication that night had come. They were now going up and at an angle which was very perceptible. The boys had become quite expert in detecting certain activities, as they tried in every way to understand the use of the signals. One thing was certain; two sets of bells were brought into play as the signal for changing the motive power. The first signal, three bells followed by two more, was invariably the necessary preparation for this event.
A highly pitched bell next gave the signal to stop the gasoline engines and a deep-toned bell indicated the coupling of the electric motor. Occasionally a new set of signals would resound, which they tried to figure out. During the night Alfred thought he had found the key.
"Did you notice the big hand wheel on the side of the upright tank, which we pass as we go into the dining room?" he remarked.
"That is connected with a large valve," said the captain. "What did you observe?"
"Well, did you ever notice that before they rang the shrill bell four times we always have heard a whistle?" asked Alfred.
"Why, I have heard the bell ring four times on several occasions without the whistle," contended Ralph.