[Illustration: The searchlight revealed a huge circular turret with a pair of monster guns. Slowly the submarine swung round, the light travelling the length of the huge mass of weed-encrusted iron and steel.]
Captain Brookes addressed them in a few words, urging the men to carefully consider the step they were taking.
"You will," he continued, addressing Lieutenant Palmer, "descend for not more than one hour. If at the end of that time the submarine does not reappear I must take it for granted that some mishap has befallen you—which Heaven forfend. Meanwhile, all of you will do well to take a quarter of an hour's rest. Should any man, during that interval, think better of his decision, he may withdraw."
When the little crew were dismissed Gerald retired to the seclusion of his cabin. What he did during those fifteen minutes no human being knew, though many hazarded a guess that was not far from the truth.
Then, having shaken hands with his messmates and received their good wishes for the enterprise—though the proceedings savoured of a party of doomed men setting out for execution—the five members of the submarine's crew descended to the orlop deck and entered the vault-like cavity of the steel cylinder.
Hardly a word was spoken during the descent, save when, from time to time, Palmer's voice could be heard speaking slowly and deliberately into the wireless telephone to acquaint the Olive Branch of the submarine's downward progress.
Circling in wide curves the steel monster plunged slowly downwards. Every moment the pale green light that filtered through the sunlit sea grew dimmer, while as the pressure increased the revolution of the propeller became slower and slower.
At thirty-five fathoms the wireless telegraphy became useless, while the darkness became so opaque that the powerful electric searchlight in the conning-tower had to be switched on. By the aid of its gradually diverging beams Gerald could see a waste of water, boundless, trackless, lifeless. Sixty fathoms. The motor was running most abominably, emitting long sparks as the increased resistance of the water strove to stop the already slow-running propeller-blades.
"What's that?" hissed Palmer, pointing to a thick, indefinite line intercepting the rays of the searchlight.