is about 20 percent of the time-interval between successive frames; this improves resolution and smear when rapidly-growing fireballs are photographed. The carnera may be run at speeds up to about 3,000 frames per second, and the total running time is less than two seconds. For the Pinon. shot we plan to run the cameras at about 2,000 frames per second. The Eastman camera utilizes a single electrical motor, which drives the film-advance sprocket wheel, the rotating prism, and the take-up spool. Suitable gears are provided to run the prism, and a friction clutch drives the take-up spool. The motor is of the universal ac/dc-type, operating from batteries totaling 120 volts as we use it. The current required is about 40 amperes initially, falling to about 12 amperes at the end of the run. An integral timer removes resistance in the motor circuit as the speed increases, so optimizing the startup time without breaking film under the stress of sudden acceleration. Speed and operating time may be adjusted within limits by choice of initial and final positions of the Ohmite rheostat and also by changing the supply voltage. The camera is provided with a focusing telescope, arranged to view the image in the film-plane from behind, This accessory is not used for focusing purposes, but does provide a visual check to camera aiming. 10, Lenses A series of lenses is available for use with the Eastman High-Speed camera, ranging from 25 mm to 500 mm in focal length. The distance from the mounting flange to emulsion is 1:489, 0.001 inches. The pres- ence of the rotating prism requires that the back focal distance (from rear element to film-plane) be at least 0.495 inches, and further introduces distortion when lenses of very short focal length are employed. In fact it is always necessary to correct for distortion effects whenever lenses shorter than 40 mm are used. It has been seen that the Pifion fireball might grow to a diameter of approximately 2,700meters, at the end of the useful portion of the growth. If we place the camera 100,000 ft from the burst, and if we ask that the image of thd 2,700-meter fireball be approximately5 mm_in diameter, we -_——.- find that a lens of about 60 mm focal length is needed. We will consequently use the 63-mm Ektar F/2 ciné lens, manufactured by Eastman Kodak Company. ed The resulting image will be 4.2 mm,in diameter, and the overall Ce -*4.-