There the wheel was given to Dan, and Nelson took Bob below and initiated him into the mysteries of the gas engine. Nelson started at the gasoline tank, and traced the flow of the fuel until it had passed through the cylinders and was discharged at the exhaust. Carburetor—or, in the present case, vaporizer—pump, oil cups, spark plug, and clutch were duly explained, and then Nelson took up the ignition, starting at the battery and following the wires to the engine. Finally, the motor was stopped, the gasoline shut off, and Bob was allowed to start things up again. Of course, he didn’t succeed the first time, nor the second, but in the end he did, and was as pleased as could be. For the rest of the afternoon he stayed in the engine room—while Dan and Tom had a beautiful time on deck running the boat to suit themselves—and by the time they reached their anchorage again Bob had qualified, to his own satisfaction at least, as a gas engineer. “It’s simple enough when you understand it, isn’t it?” he asked earnestly. “Yes,” laughed Nelson; “there’s nothing to it at all—until the engine stops and you can’t find out why!” They had dinner at the Harborside again, and in the evening wrote home to their folks on the lovely stationery with the crossed flags. And at half-past nine, everyone having personally assisted at the lighting of the riding light, they turned in and slept like logs until morning. CHAPTER VI—IN WHICH THEY FOLLOW A RACE “Well!” exclaimed Bob. “Look at the boats!” The _Vagabond_ was cutting her way through the sunlit waters at the best pace of which she was capable—“easily twelve miles an hour, I’ll bet you,” according to Nelson. Bob had the wheel, and was turning to port as the point drew abreast. Once around the lighthouse, the harbor lay before them blue and sparkling in the morning sunshine, and as full of boats as a raisin pie of raisins. Even Tom, eminently matter of fact, drew his breath as the _Vagabond_ dashed across the harbor mouth. Marblehead Harbor is naturally one of the most beautiful on the coast, and this morning, thronged with yachts of all descriptions, swinging at their moorings, cream-white sails aflutter in the light breeze, flags flying everywhere, paint and varnish glistening and brasswork catching the sunlight on every side, it presented as fair a sight as one is apt to find. Between the white and black and mahogany-red hulls of the yachts busy, cheerful, impertinent launches darted in and out, filling the air with the sharp explosions of their engines. On one side the quaint old town came tumbling down to the wharves and the dripping seawall, a delightful hodgepodge of weather-stained sheds and whitewashed houses. On the other, green lawns set with summer cottages and shaded by vividly green elms stretched from the distant causeway to where the shore broke into a rocky promontory, from which the stone and shingle house of the Corinthian Yacht Club arose as though a part of the natural scenery.