They walked along the path and disappeared from sight. It was an hour before they were seen again. Then from round the shoulder of the cliff there suddenly came into view a thing resembling a monstrous grasshopper in flight, and through the air sounded a low grinding hum. The servants rushed into the compound; the miners at work in the open uttered a shrill cry, which brought their comrades in a flock from the galleries; and they stood at gaze as the strange machine wheeled into the gorge, and flew, skimming the river, until it was lost to sight. "Marvellous achievement, sir," said Ditta Lal at Mr. Appleton’s elbow. Mr. Appleton did not answer: there was a look of anxiety upon his face. "I perceive, sir," said the Babu, "that your countenance is sicklied o’er with pale cast of apprehension. Nothing is here for tears; in short, there is nothing to be afraid of; I have worked it out. Engine makes 1500 revolutions per minute: propeller geared down to 750: ascensional velocity, by my calculations----" "Your calculations be hanged!" cried Mr. Appleton, whose wonted urbanity gave way under the strain of Ditta Lal’s loquacity. "Get out!" Ditta Lal looked hurt, but tried to smile. It was an hour before the aeroplane reappeared, and another hour before the boys rejoined their uncle. "We made a splendid flight," said Bob, who was in the highest spirits. "Everything worked perfectly. You must come for a trip yourself, Uncle." "No, thank you. I am vastly relieved to see you back safe and sound. The Babu has begun calculating again, and got on my nerves." "Calculating, is he?" said Lawrence. "I should have thought he had had enough of that. I wonder if we can cure him." He called to Ditta Lal, who was standing at the door of his store-shed. "What weight do you suppose the aeroplane will carry?" he asked. "I do not suppose, sir," replied the Babu. "I have worked it out. Permit me to express jubilation at successful trip, sir. You ask about weight." He drew a paper from his pocket. "Here are correct figures. You can carry fifteen hundred and eighty-six pounds six ounces, with four decimals of no account." "What do you scale, Bob?" asked Lawrence. "Twelve stone two." "I’m eleven stone eight: together we make about three hundred and thirty pounds. Ditta Lal, _there’s just room for you_!" For a moment the Babu looked puzzled. Then he said: "It is human to err, sir. I must have made trifling error in my additions. I revise my calculations." And he went away, evidently determined to discover either that the aeroplane would not support so great a load as he had calculated, or that his own weight considerably exceeded twelve hundred pounds.