"No wonder, after all you've done," said Genevieve. She added, with a radiant smile, "But isn't it glorious that you've finished such a great work! Papa says that you've actually invented a new kind of dam."
The silent footman had reappeared with another plate and glass of wine. He glided around behind Blake, who had leaned forward again with the right arm upon the edge of the table. Unconscious of the servant, who placed the plate and wine glass near him on his left and quietly glided from the room, the engineer responded to Genevieve's remark with an animation that might have been likened to the last flare of a dying candle.
"No," he said, "it's not exactly a new kind of dam—not an invention. I did work out once a modification of bridge trusses which some might call an invention,—new principle in the application of trusses to bridge structure. Allows for a longer suspension span on cantilever bridges."
"But this Zariba Dam," remarked Lord James; "I've yet to learn, myself, just how you worked it out."
"Well, it wasn't any invention; just a sort of discovery how to combine a lot of well-known principles of construction to fit the particular case. You see, it's this way. There was only one available site for the dam, and the mid-section of that was bottomless bog; yet provision had to be made for a sixty-five foot head of water."
"You take him, Miss Genevieve," said Lord James. "They have no solid ground to build on, and the water above the dam is to be sixty-five feet deep."
"I should think the dam would sink into the bog," remarked Genevieve.
"That was one factor in the problem," said Blake. "Solved it by putting the steel reinforcement of the concrete in the form of my bridge-truss span. The whole central section could hang in midair and not buckle or drop. That was simple enough, long's I had my truss already invented. The main difficulty was that deep bog. If you studied hydrostatics, you'd soon learn that a sixty-five foot head of water puts an enormous pressure on the bed of a reservoir."
Absorbed in his explanation, Blake unconsciously grasped the wine glass in his left hand, as he went on:
"That pressure would be enough to make the water boil down through the bog and clear out under the deepest foundation any of the other engineers had been able to figure out. Well, I figured and figured, but somehow I couldn't make anything in the books go. At last, when I had almost given up—"