"So that I can work in that solarium to-night without interruption," replied Dr. Bird. "I have some tests which I wish to carry out while it is still dark. If my results are negative, forget what I have told you. If they yield any information, I will be glad to share it with you at the proper time. Now get the President out of that solarium and tell me when the coast is clear." The Admiral donned a dressing gown and stepped out of the room. He returned in fifteen minutes. "The solarium is at your disposal, Doctor," he announced. "Shall I accompany you?" "If you wish," assented Dr. Bird as he picked up his apparatus and strode out of the room. In the solarium he glanced quickly around, noting the position of each of the articles of furniture. "I presume that the President always sleeps with his head in this direction?" he remarked, pointing to the pillow on the disturbed bed. The Admiral nodded assent. Dr. Bird opened the bag which he had packed in his laboratory, took out a sheet of cardboard covered with a metallic looking substance, and placed it on the pillow. He stepped back and donned a pair of smoked glasses, watching it intently. Without a word he took off the glasses and handed them to the Admiral. The Admiral donned them and looked at the pillow. As he did so an exclamation broke from his lips. "That plate seems to glow," he said in an astonished voice. * * * * * Dr. Bird stepped forward and laid his hand on the pillow. He was wearing a wrist watch with a radiolite dial. The substance suddenly increased its luminescence and began to glow fiercely, long luminous streamers seeming to come from the dial. The Doctor took away his hand and substituted a bottle of liquid for the plate on the pillow. Immediately the bottle began to glow with a phosphorescent light. "What on earth is it?" gasped Carnes. "Excitation of a radioactive fluid," replied the Doctor. "The question is, what is exciting it. Somebody get a stepladder." While Bolton was gone after the ladder, the Doctor took from his bag what looked like an ordinary pane of glass. "Take this, Carnes," he directed, "and start holding it over each of those panes of quartz which you can reach. Stop when I tell you to." * * * * * The operative held the glass over each of the panes in succession, but the Doctor, who kept his eyes covered with the smoked glasses and fastened on the plate which he had replaced on the pillow, said nothing. When Bolton arrived with the ladder, the process went on. One end and most of the front of the solarium had been covered before an exclamation from the Doctor halted the work. "That's the one," he exclaimed. "Hold the glass there for a moment." Hurriedly he removed the plate from the pillow and replaced the phial of liquid. There was only a very feeble glow. "Good enough," he cried. "Take away the glass, but mark that pane, and be ready to replace it when I give the word."