"As to that," the captain responded, "it is impossible to answer in a single word. The most of our operations are in rivers and harbors, or in bays more or less shallow. Sometimes at sea it is necessary to examine the bottom of a ship, in order to stop a leak or repair some other damage. In such a case the ship is stopped, and a ladder is lowered near the place to be examined; a man goes down in his submarine armor without difficulty, and, though the water must be reasonably smooth to allow him to do so safely, I have known it to be done when there was quite a heavy sea on. The general rule is, that, unless the sea is smooth enough to allow a boat to lie along side for the purpose of assisting the diver, it is not wise to send him below. Divers are their own judges of such matters, and will naturally refuse to descend if the risk is too great.
"Once in awhile we have cases of diving in the open ocean. Do you remember the loss of the steamship Japan, on the coast of China, in December, 1874?"
The boys said they had heard about it while they were in China, but could not remember anything particular about the affair.
"Well," continued the captain, "the Japan was burnt at sea, one hundred and thirty-five miles north-east of Hong-kong, and fifty miles from Swatow. The nearest land was Breaker Point, twenty miles away, and the water where the wreck sunk was twenty-three fathoms, or one hundred and thirty-eight feet deep. The Japan had about three hundred and fifty thousand dollars in silver on board, and the underwriters at Hong-kong who had insured it determined to make an effort for its recovery. For this purpose they engaged Captain Roberts, who was a well-known wrecker on the coast of China, and set him at work.
"A schooner and a small steamer were bought, and in January, 1875, Captain Roberts began looking for the wreck. He dragged the bed of the ocean for four or five weeks before he found anything; but at last he was successful, and discovered one of the paddle-wheels of the ship. It was some time later before he found the wreck of the ship, as it proved to have drifted eleven miles south-west of the spot where the wheel had dropped off."
"How could that be?" Frank exclaimed.
"It was because the wind was blowing very strong at the time from the north-east, and after the wheel fell off the ship was driven on before the gale till it had burnt low enough to sink. It took from March to July to find the wreck after the wheel was discovered, and then they immediately began operations for getting at the sunken treasure.
"The south-west monsoon blows from March till September, and it was only during this monsoon that the divers could work. On the 12th of that month the monsoon ceased, and Captain Roberts had not been able to get at the treasure, which was contained in an iron tank in the hold of the ship. He thought the whole enterprise would end there, and the Japan and her three hundred and fifty thousand dollars would remain undisturbed at the bottom of the sea. It was not likely that the underwriters would incur the expense of another expedition the following year, when the chances of recovering anything were so doubtful.
"The diver went down for the last time; and while he was below the crew were making preparations to hoist anchor, and be off for Hong-kong as soon as he rose.