Finishing as quickly as he could, he put out our sole electric light, unscrewed the bulb and attached to the socket a wire which he had connected with the instrument over which he had spent so many precious moments.
Through the little porthole he cast a peculiar disk, heavy, such as I had seen him place so carefully aboard the Uncas.
It sank in the water with a splash and trailed along beside the yacht, held by a wire, submerged, perhaps, ten or twelve feet.
He made a final inspection of the thing as well as he could by the light of a match, then pressed a key which seemed to close a circuit.
I could feel a dull, metallic vibration, as it were.
"What are you doing?" I asked, looking curiously also at an arrangement, like a microphone, which he had placed over his ears.
"It works!" he cried excitedly.
"What works?" I reiterated.
"This Fessenden oscillator," he explained. "It's a system for the employment of sound for submarine signals. I don't know whether you realize it, but great advance has been made recently since it was suggested to use water instead of air as the medium for transmitting signals. I can't stop to explain this apparatus just now, but it is composed of a ring magnet, a copper tube which lies in an air gap of a magnetic field, and a stationary central armature. The magnetic field is much stronger than that in the ordinary dynamo.
"The copper tube, which has an alternating current induced in it, is attached to solid disks of steel which in turn are attached to a steel diaphragm an inch thick. In the Uncas I had a chance to make that diaphragm practically a part of the side of the ship. Here I have had to hang it overboard, with a large water-tight diaphragm attached to the oscillator."