The Poisoned Pen [112]
on La Montaigne. "I knew we should need some means to communicate with Herndon," he explained simply, "and the wireless telephone wasn't practicable. So I have used Dr. Alexander Graham Bell's photophone. Any of the lights on this side of La Montaigne, I knew, would serve. What I did, Walter, was merely to talk into the mouthpiece back of this little silvered mirror which reflects light. The vibrations of the voice caused a diaphragm in it to vibrate and thus the beam of reflected light was made to pulsate. In other words, this little thing is just a simple apparatus to transform the air vibrations of the voice into light vibrations. "The parabolic reflector over there catches these light vibrations and focuses them on the cell of selenium which you perhaps noticed in the centre of the reflector. You remember doubtless that the element selenium varies its electrical resistance under light? Thus there are reproduced similar variations in the cell to those vibrations here in this transmitter. The cell is connected with a telephone receiver and batteries over there and there you are. It is very simple. In the ordinary carbon telephone transmitter a variable electrical resistance is produced by pressure, since carbon is not so good a conductor under pressure. Then these variations are transmitted along two wires. This photophone is wireless. Selenium even emits notes under a vibratory beam of light, the pitch depending on the frequency. Changes in the intensity of the light focused by the reflector on the cell alter its electrical resistance and vary the current from the dry batteries. Hence the telephone receiver over there is affected. Bell used the photophone or radiophone over several hundred feet, Ruhmer over several miles. When you thought I was talking to myself I was really telling Herndon what had happened and what to do - talking to him literally over a beam of light." I could scarcely believe it, but an exclamation from Kennedy as he drew his head in quickly recalled my attention. "Look out on the river, Walter," he cried. "The Mohican has her searchlight sweeping up and down. What do you see?" The long finger of light had now come to rest. In its pathway I saw a lightless motor-boat bobbing up and down, crowding on all speed, yet followed relentlessly by the accusing finger. The river front was now alive with shouting. Suddenly the Mohican shot out from behind the pier where she had been hidden. In spite of Lang's expertness it was an unequal race. Nor would it have made much difference if it had been otherwise, for a shot rang out from the Mohican which commanded instant respect. The powerful revenue cutter rapidly overhauled the little craft. A hurried tread down the passageway followed. Cases were being shoved aside and a key in the door of our compartment turned quickly. I waited with clenched fists, prepared for an attack. "You're all right?" Herndon's voice inquired anxiously. "We've got that steward and the other fellows all right." "Yes, come on," shouted Craig. "The cutter has made a capture." We had reached the stern of the ship, and far out in the river the Mohican was now headed toward us. She came alongside, and Herndon quickly seized a rope, fastened it to the rail, and let himself down to the deck of the cutter. Kennedy and I followed. "This is a high-handed proceeding," I heard a voice that must have been Lang's protesting. "By what right do you stop me? You shall suffer for this." "The Mohican," broke in Herndon, "has the right to appear anywhere from Southshoal Lightship off Nantucket to the capes of the Delaware, demand an inspection of any vessel's manifest and papers, board anything from La Montaigne to your little motor-boat, inspect it, seize it, if necessary put a crew on it." He slapped the little cannon. "That commands respect. Besides, you were violating the regulations - no lights." On the deck of the cutter now lay four cases. A man broke one of them open, then another. Inside he disclosed thousands of dollars' worth of finery, while from a tray he drew