The lieutenant smiled at the boy's eagerness, but filled his pipe and began.

"Right opposite Smith's Point," he said, "on the Virginia shore, the tides and currents at the mouth of the Potomac River and at the entrance of Chesapeake Bay have built out a shoal which, if you remember your chart, you will recall juts out in the bay over nine miles from the land. The same tides had scoured Smith's Island on the other hand—port side going out of the bay, but there are some nasty rocks in the channel. It's a tricky spot, that Smith's Point Shoal, and many a good vessel has gone to pieces on it.

"It was the wreck of the barque Mary Louise that drew public attention to Smith's Point. She struck the shoal and went down with all hands. Less than two hours after she sank, a steamer came along and hit the wreckage. The steamer was so badly injured that it was only by a good deal of luck and clever handling that her captain succeeded in beaching her and saving all the passengers. The Lighthouse Board had made several recommendations for the erection of a lighthouse at that point, and when public attention had been focussed to this danger by the disaster, it was easy enough to get the appropriation through Congress. So the money was set aside and Father was given the contract of designing and erecting the lighthouse.

"By the end of the next month a huge unwieldly foundation caisson was on the ways at a shipyard in Baltimore. I was just a kid at the time, but the queer shape of this interested me right from the start. It was like a bottomless box, thirty-two feet square on the inside and twelve feet high. It was so thick that a tall man could lie down crosswise on one of the walls and stretch out his arms to the full, and then there would be several inches beyond the tips of his fingers and the ends of his feet."

"My word," said Eric, "it must have had some timber in it!"

"It had a lot of weight to support," said the other. "After a while, it was launched—I was there—and dropped into the bay near Sparrow's Point. On it were built the first two courses of the iron cylinder which was to be the lower part of the lighthouse. Although that wooden caisson weighed over a hundred tons, so heavy and solid was the cylinder that it sank the wooden structure out of sight."

"How big was the cylinder?" queried the boy.

"It was thirty feet in diameter and each of the courses was six feet high. That's twelve feet for the two courses. Inside the big cylinder was a second smaller one, like an air-shaft, five feet in diameter. A pump was rigged on the edge of the cylinder for the journey down the bay, in case any water should splash over the sides from the wake of the tug.

"When the springtime came and there was a reasonable prospect of fair weather, quite a fleet set out for Baltimore with Father and me in the leading tug. I felt as proud of myself as if I'd been an admiral! I wasn't quite sure," he added, laughing, "whether Father was the boss of the job or whether I was, myself.

"We had a large ocean-going tug towing the caisson, but we went ahead at very slow speed. Besides the big tug there were two tugs towing seven barges with the iron work, with building materials, stone, cement, and all that sort of thing. It made quite a gallant show.