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. Gerald looked, then thrusting the vessel's rudder over slightly, he allowed the submarine to glide past the obstruction. "It's one of the grapnel lines." "Impossible!" "Yes, you've forgotten the magnifying power of the water. It shows we are not far out of our course." "All right down there, Halliday?" "Aye, aye, sir." "Inform me the moment there's any sign of the plates yielding." "Very good, sir." The seaman was perfectly cool. Implicitly he trusted the two officers in the conning-tower, though he knew that now at any moment the massive steel structure might be crushed like an egg-shell by the tremendous weight of water without. Suddenly, at sixty-five fathoms, Palmer seized the reversing lever and brought the forward motors of the craft to a standstill. Both he and Gerald saw a sight that filled them with nameless awe. It was as if the submarine was heading straight for the summit of a mountain--a mountain of weed and barnacles covering an object that was not the work of Nature--it was the work of man.