"That is another of our new processes," he added after a moment's reflection. "Echo—that's the answer in a nutshell."
The captain led the way to the ship's marimeter, a cylindrical contrivance that looked as though it might house a compass or a binnacle lamp.
"The marimeter works on the principle of electricity controlled by sound vibration," the captain expounded in his competent fashion. "A sound wave is sent out from the bottom of the vessel by mechanical means and the instant this sound is started it is picked up electrically and relayed to the recording instrument and the dial of the latter begins to register. The sound wave travels to the bottom of the ocean and returns in the form of an echo, and this echo is also picked up by the diaphragm in the bottom of the boat and is also relayed by electricity to the recording instrument, causing the pointer to stop immediately. Sound travels at practically a uniform rate in the water, at about 4000 feet a second. The depth is measured by accurately taking and recording mechanically the time for sound to travel down and back. The depth is shown on the dial in fathoms, and four soundings may be made per minute."
It all sounded so simple, and yet what a wonderful contrivance as against the old-fashioned method of taking deep-sea soundings. To demonstrate Captain Austin took an electrical sounding for his new protegées and in a few seconds the "echo" had returned from the bottom of the Sound, showing a depth of ten fathoms.
For some hours, under the guidance of the ship's skipper, the trio of newcomers thoroughly inspected the Nemo. This plainly was the "prospecting" boat of the salvage company's fleet. It went out and staked the claim and then called on the full facilities of the fleet for completion of the job.
Captain Austin, completely won by the honesty and candor of his new friends, and acting under instructions of superintendent Brown, took the boys entirely into his confidence.
"I do not mind telling you that we are after high stakes this trip," he told them. "An English steamship, the Dominion, was sunk off Martha's Vineyard late in 1916. She had among her cargo a quantity of gold bullion and South African diamonds. She took fire after being shelled by a German submarine and was making a run for the coast when she went down. She is between two and three hundred feet down and it is our job to look her over for the next few days and report back to Bridgeford on our findings."
The news of impending action was joyously received by Jay and Dick, who declared they were ready on a moment's notice to take their first dip into the blue for their new employers. What! thirty dollars a day, and the chance to win a percentage on any treasure actually reclaimed! It was a wonderful opportunity, to their minds.
"Better take a look over your diving equipment and see that everything is all right," suggested the ship's captain. Jay and Dick accordingly went thoroughly over their outfits during the next few hours, finding suits, shoes, helmets and air-line connections quite up to the standard of the latest improved diving equipment.