I saw him cast a quick glance at the others.  For the moment Dominick, Gage, and Kinsale seemed to have forgotten us in their interest explaining to Norma what had been accomplished in her absence.  He seized the occasion to make an even closer examination of the complicated apparatus.  So carefully had accident been guarded against that even a device for the purification of the air had been installed in the machine which forced the fresh air down to the diver, compressed.

It was this apparatus which I saw Kennedy studying most, especially one part where the air was passed through a small chamber containing a chemical for the removal of carbon dioxide.  As he looked up, I saw a peculiar expression on his face.  Quickly he removed the chemical, leaving the tube through which the air passed empty.

“I think the air will be pure enough without any such treatment,” he remarked, glancing about to be sure no one had observed.

“How is that?” I inquired, eagerly.

“Well, you know air is a mechanical mixture of gases, mainly oxygen and nitrogen.  Here’s something that gives it an excess of nitrogen and a smaller percentage of oxygen.  Nitrogen is the more dangerous gas for one under compressed air.  It is the more inert nitrogen that refuses to get out of the blood after one has been under pressure, that forms the bubbles of gas which cause all the trouble, the ‘bends,’ compressed-air sickness, you know.”

“Then that is how Traynor died?” I whispered, coming hastily to the conclusion.  “Some one placed the wrong salt in there—­took out oxygen, added nitrogen, instead of removing carbon dioxide?”

Norma had turned toward us.  It was too early for Kennedy to accuse anybody, whatever might be his suspicions.  He could not yet come from under cover.  “I think so,” was all he replied.

A moment later the group joined us.  “No one has been down on the wreck yet?” inquired Craig, at which Everson turned quickly to the three companions he had left in charge, himself anxious to know.

“No,” replied Kinsale before any one else could answer.  “Mr. Dominick thought we’d better wait until you came back.”

“Then I should like to be the first,” cut in Craig, to my utter surprise.  Remonstrance had no effect with him.  Neither Norma nor Asta could dissuade him.  As for the rest of us, our objections seemed rather to confirm him in his purpose.

Accordingly, in spite of the danger, which now no one no more than he knew, all the preparations were made for the first dive.  With the aid of Kinsale, whom I watched closely, though no more so than Craig, he donned the heavy suit of rubberized reinforced canvas, had the leads placed on his feet and finally was fitted with the metal head and the “bib”—­the whole weighing hardly short of three hundred pounds.  It was with serious misgiving that I saw him go over the side of the trawler and shoot down into the water with its dark mystery and tragedy.