By the time the story was ended the boat was at the side of the steamer, and our friends were speedily on board. In a little while the captain had completed his business at Pooree, and the vessel steamed away in the direction of Calcutta. Pooree was the last port visited on the voyage from Colombo to Calcutta. When the boys went on deck in the morning the captain said they were in sight of land; Frank and Fred looked around, but could see nothing save the waters extending in every direction, with a few sails in sight here and there. The captain observed their perplexity, and smiled as he said, "We are in sight of the Sand Heads; you have heard of the Sand Heads at the month of the Hoogly River, have you not?" "Certainly," Frank answered; "but I cannot see them." "Well," continued the captain, "they are under water where you see that brig anchored a couple of miles ahead of us. We consider that land is in sight when we see the pilot-brig, though we cannot see any land at all. The Sand Heads are banks of sand beneath the water, and the brig marks their locality. At the brig the steamer goes into the charge of the pilot, and my authority over her course ceases." As they neared the brig a small boat came off; the ladder was lowered from the side of the steamer, and the pilot climbed to the deck, followed by his servant and baggage; then the small boat dropped astern, and the steamer continued on her way. Soon a buoy was in sight, and then another and another, in a winding line, and the boys learned that the channel through the treacherous sands was thus indicated long before land could be seen. "You see what an excellent means of defence we have in case of war," said the captain of the steamer. "We have only to take up the buoys, and no hostile fleet could find its way inside, even if it had the aid of all the pilots in the service. No one can follow the channel without these buoys, no matter how often he may have been over the route. The maintenance of the harbor of Calcutta and its approaches is a matter of great expense, and has been a puzzle to the best engineers. Even after we enter the river we have many difficulties to encounter, and the pilot needs a pair of sharp eyes, and must keep them well open." [Illustration: BAYOU IN SAUGUR ISLAND.]