"Everything will be ready for you, Doctor, but I confess that I don't know what it is all about." "It's the biggest case you ever tackled, old man, and I hope that we can pull it off successfully. I'd like to go over it with you now, but I'll be busy at the Bureau for the rest of the night. Drop me off there, will you?" At sunrise the next morning, Bolton met Dr. Bird at the entrance to the White House grounds. "Where is your detail?" he asked. "In the State, War and Navy Building." "Good. I want to go to the solarium, put a light on the place where the President's pillow was last night, and mark that pane of quartz we were looking through. Then we'll join the detail." * * * * * Dr. Bird placed the light and walked with Carnes across the White House grounds. Bolton's badge secured admission to the State, War and Navy Building for the party and they made their way to the office of the Assistant to the Adjutant General. "Did you mark the pane of glass through which you flashed your light last night, Bolton?" asked the Doctor. The detective touched one of the panes. "Good," exclaimed the Doctor. "I notice that this window has hooks for a window washer's belt. Get a life belt, will you?" When the belt was brought, the Doctor turned to Carnes. "Carnes," he said, "hook on this life saver and climb out on the window ledge. Take this piece of apparatus with you." He handed Carnes a piece of apparatus which looked like two telescopes fastened to a base, with a screw adjustment for altering the angles of the barrels. * * * * * Carnes took it and looked at it inquiringly. "That is what I was making at the Bureau last night," explained Dr. Bird. "It is a device which will enable me to locate the source of the beam which was reflected from this pane of glass onto the President's pillow. I'll show you how to work it. You know that when light is reflected the angle of reflection always equals the angle of incidence? Well, you place these three feet against the pane of glass, thus putting the base of the instrument in a plane parallel to the pane of glass. By turning these two knobs, one of which gives lateral and the other vertical adjustment, you will manipulate the instrument until the first telescope is pointing directly toward the President's pillow. Now notice that the two telescope barrels are fastened together and are connected to the knobs, so that when the knobs are turned, the scopes are turned in equal and opposite amounts. When one is turned from its present position five degrees to the west, the other automatically turns five degrees to the east. When one is elevated, the other is correspondingly depressed. Thus, when the first tube points toward the pillow, the other will point toward the source of the reflected beam." "Clever!" ejaculated Bolton.