"Splendidly; quite as well as you can hear me, I should say," replied Sir Reginald. "I congratulate you, Professor, upon the success of your latest invention. It is a most useful instrument; and I can easily imagine a number of circumstances under which it might prove of the utmost value to us. An idea has just occurred to me. How would it do, while we are about it, to ascertain the greatest distance at which it is possible to communicate intelligibly with each other?" "Excellent!" answered von Schalckenberg. "We will shut ourselves in, ascend to a height of ten thousand feet, into the calm belt, and then proceed at full speed directly away from you. Keep your finger on the black button of your instrument, please, for our guidance; and when our bell ceases to sound we shall know that we have lost touch with you." "Right!" came the answer. And instantly all the bells in the ship again started ringing. At the same moment the professor closed the door and windows of the pilot-house, and injected a strong jet of vapour into the air-chambers, causing the ship to rise rapidly into the air. Then he sent the engines full speed ahead, and pointed the ship's sharp snout on a compass bearing that left the party on the beach directly astern of her. For three-quarters of an hour the bells in the ship continued to ring, at first strongly, and then gradually with diminishing strength; and finally, when the ship had been running continuously at full speed for fifty minutes, they became inaudible. The professor's face, meanwhile, was a picture of ever-growing delight. "If we can continue to hear the bell for a quarter of an hour I shall be quite satisfied," he had remarked to Mildmay, as the ship first rose into the air; "for by that time we shall be quite fifty miles distant from the beach." And when the quarter of an hour had elapsed with no perceptible diminution in the volume of sound, his growing satisfaction had been faithfully mirrored by the steadily expanding smile upon his expressive features. Finally, when at length the bells ceased to ring, he exclaimed-- "Well! who would have believed it? Here have I, a poor silly scientist, been hoping that my little invention would prove effective for as long a distance as fifty miles; and behold, at the distance of one hundred and twenty miles from our friends we have only just lost touch with them. Let us try back, my friend; turn the ship round, and we will then note how far we have to run before we can speak clearly to each other."