“This suit might be very valuable to the government,” he exclaimed to Eva.  “I am going to try it myself.”

“Please don’t,” pleaded Eva.  “It isn’t worth it.  It’s not worth the risk.”

Locke, however, realized that here was something of extreme importance, and as he visualized to Eva the helplessness of a deep-sea diver, his air-line cut, struggling in vain to release himself and rise to the surface, he began to win her over.

At the moment when Quentin and Eva were in the library, Zita was taking advantage and was ransacking Locke’s laboratory, not with any definite purpose in mind, but searching in every nook for some clue which might tell her what he was about.

The speed with which she worked was extraordinary.  Yet, before she moved an instrument, a retort, a book, its position was minutely studied, so that she could restore it to its former place without any one suspecting that it had ever been moved.

It was while she was thus occupied that her eye fell upon an instrument which aroused in her an excited interest.  It was very like the headpiece used by operators of telephones, and she hastened to adjust it.  In a moment it was as though she were in the library.  She could hear Locke’s earnest laugh and in it Zita could detect an undercurrent of tenderness.  Her lips compressed and her eyes hardened as she listened.  Locke was speaking about a letter and it seemed to be something important.  Zita was all ears.

But Locke’s next words which she heard were his decision to test the diving-suit, and as she listened she became tense, for this information she knew was important.  The continued note of tenderness in Locke’s voice more infuriated Zita.  She removed the headpiece of the dictagraph, slammed it back into the desk drawer from which she had taken it, and hurried out.

In the library, Locke, having persuaded Eva, left her and went down into the Graveyard of Genius, where he touched the secret spring and the massive door flew open.  He entered the gloomy place and went at once to the shelf upon which lay the self-liberating diving-suit.  He took the suit down and examined its every detail minutely.  As he did so he became more and more enthusiastic and he could find no fault with any of its features.

“It’s entirely practical,” he exclaimed to himself.  “I’m going to try it to-day.”

He closed the great door and remounted the stairs, carrying the suit with him.  But had he noticed the fiery eyes that had watched him through the secret rock door of the cavern he would not have been so eager to try the test he had in mind.

By this time Eva had called her car, and together Locke and Eva drove to the near-by cove, where there was a little launch which he planned to use.

Out into the river they sailed, Eva at the wheel, while Locke busied himself over the sputtering engine.  Soon they arrived at a spot which was suitable for the test of the suit.