"It is rather crude and may not be accurate enough to locate the source exactly, but at least it will give us a pretty good idea of where to look. Given time, a much more accurate instrument could have been made, but two telescopic rifle sights and a theodolite base were all the materials I could find to work with. Climb out, Carnesy, and do your stuff." * * * * * Carnes climbed out on the window and fastened the hooks of the life saver to the rings set in the window casings. He sat the base of the instrument against the pane of glass and manipulated the telescope knobs as Dr. Bird signalled from the inside. The scientist was hard to please with the adjustment, but at last the cross hairs of the first telescope were centered on the light in the solarium. He changed his position and stared through the second tube. "The angle is too acute and the distance too great for accuracy," he said with an air of disappointment. "The beam comes from the roof of a house down along Pennsylvania Avenue, but I can't tell from here which one it is. Take a look, Bolton." The Chief of the Secret Service stared through the telescope. "I couldn't be sure, Doctor," he replied. "I can see something on the roof of one of the houses, but I can't tell what it is and I couldn't tell the house when I got in front of it." "It won't do to make a false move," said the Doctor. "Did you arrange for that plane?" "It is waiting your orders at the field, Doctor." "Good. I'll go up to the office of the Chief of Air Service and get in touch with the pilot over the Chief's private line. There are some orders that I wish to give him and some signals to be arranged." * * * * * Dr. Bird returned in a few minutes. "The plane is taking off now and will be over the city soon," he announced. "We'll take a stroll down the Avenue until we are in the vicinity of the house, and then wait for the plane. Carnes will take five of your men and go down behind the house and the rest of us will go in front. Which building do you think it is, Bolton?" "About the fourth from the corner." "All right, the men going down the back will take station behind the house next to the corner and the rest of us will get in front of the same building. When the plane comes over, watch it. If you receive no signal, go to the next house and wait for him to make a loop and come over you again. Continue this until the pilot throws a white parachute over. That is the signal that we are covering the right house. When you get that signal, Carnes, leave two men outside and break in with the other three. Get that apparatus on the roof and the men who are operating it. Bolton and I will attack the front door at the same time. Does everybody understand?" Murmurs of assent came from the detail. "All right, let's go. Carnes, lead out with your men and go half a block ahead so that the two parties will arrive in position at about the same time."