fitted with a piston geared to an electric motor. From the tank, tubes ran to four hollow pipes, an inch and a half in diameter, which ran through the skin and extended thirty inches from the outer skin of the twenty-foot sphere. Dr. Bird stood near talking with the executive officer of the ship and from time to time giving a brief word of direction to the mechanics.
"It's safer than you might think, Commander," he said. "In the first place, that globe is not made of ordinary glass; it is made of vitrilene, a new semi-malleable glass which was developed at the Bureau and which is being made on an experimental scale for us by the Pyrex people. It is much stronger than ordinary glass, and is not sensitive to shock. It is also perfectly transparent to ultra-violet light, being superior even to rock crystal or fused quartz in that respect. The walls, as you have noticed, are four inches thick, and I have calculated that the ball will stand a uniform external pressure of thirty-five hundred atmospheres, the pressure which would be encountered at a depth of about twenty miles. I believe that it will stand a squeeze of six thousand tons without buckling, and it is impossible to fracture it by shock. It could be dropped from the top of the Woolworth Building, and it would just bounce."
"It seems incredible that it could stand such a pressure as you have named."
"My figures are conservative ones. Lambertson calculated them even higher, but we allowed for the fact that this is the first large mass of the material to be cast, and lowered them."
"BUT suppose your lifting cable should break?" objected the naval officer. "The outfit weighs a good many tons."
"You notice that the lower quarter is made of lead. The specific gravity of the entire globe when sealed up tight with two men in it is only a little more than unity. In the water its weight is so little that a three-inch manilla hawser would raise it, let alone a steel cable. I have another safety device. Granted that the cable should snap, I can detach the lead from it and it would shoot to the surface like a rocket."
"How long can you remain under water in it?"
"A week, if necessary. I have an oxygen tank and a carbon dioxide removing apparatus which will keep the air in good condition. The globe is electrically lighted, and can be heated if necessary. Should my telephone line become fouled and broken, I have a radio set which will enable me to communicate with you. I can't see that it is especially dangerous; not nearly as much so as a submarine."
"What is your object in going down, if I may ask?"
"To take pictures and to explore the wreck if we can. The globe is equipped with huge floodlights and excellent cameras. The salvage people are having a little trouble and we are trying to help them out."
"You mentioned exploring. Can you leave the globe while it is under water?"
"Yes. There is a locking device for doing so. A man in a diving suit can enter the lock and fill it with water. Once the external pressure is released he can open the outer door and step out. Coming back, he seals the outer door and the man inside blows out the lock and compressed air and then the inner door can be opened. It is the same principle as a torpedo tube."
A JANGLE of bells interrupted them and the Minneconsin slowed down. Commander Lawrence stepped to the rail and gave a sharp order to the navigating officer on the bridge. The bells jangled again and the ship's engines stopped.
"We are almost over the buoy, Doctor," he said.
Dr. Bird nodded and spoke to the two mechanics. With a few final
