Developed to help scientists determine how much sunlight is absorbed by the, earth’s atmosphere, a tiny optical instrument is being investigated by army air corps officers for possible use by pilots of bombing planes. With some slight changes it may enable the pilot to keep his plane directly between the sun and the object he is attacking, thus making it difficult for ground defenses to learn the exact position of the ship. Worn as an eyepiece, the apparatus has been used in a plane that soars to a point between a ground observer and the sun, both pilot and observer making observations of the sun’s radiation. Any difference between the two observations would be caused by the intervening amount of air and water vapor.