The Coronaviser, an Instrument for Observing the Solar Corona in Full Sunlight

of the eclipses, their short BECAUSEproblem rarity of solarinconvenient places onduration, and their occurrence usually at the earth's surface, the of observing the solar corona in full sunlight is an important one for astronomers. It is also of considerable interest to those telephone engineers who are concerned with radio transmission over long distances. The major disturbances of such transmission have their origin in the sun and studies to date have indicated that a day-to-day knowledge of the activity of the corona might prove useful in predicting the transmission conditions. The first attempt to solve this problem was made by Huggins in 1878 and since that time every conceivable optical means to accomplish the desired result has been tried. The problem is to observe the corona, not in itself a faint object, through the blinding glare of the sky in the region around the sun. If one holds his hand at arm's length so that it blots out the sun, he will find the glare in the sky around it so intense as to be painful. It is generally at least a thousand times brighter than the corona. The trials have usually been made at very high altitudes where the atmospheric glare is greatly reduced but since the scattered light from the telescope itself, particularly the objective, is some hundreds of times brighter than the corona no success was obtained until M. Lyot invented his coronographe, a telescope in which this latter kind of glare is greatly reduced. With this instrument at the top of Mt.