A high-speed shutter has been developed in order to permit photographic observation of any portion of the electrical wire explosion. The shutter consists of two parts: a fast opening part and a fast closing part. Using Edgerton's method, the fast closing action is obtained from the blackening of a window by exploding a series of parallel lead wires. The fast opening of the shutter consists of a piece of aluminum foil (approximately ** f) placed directly in front of the camera lens so that no light may pass into the camera. The opening action is obtained when a capacitor, charged to high voltage, is suddenly discharged through the foil. During the discharge the magnetic forces set up by the passage of current cause the edges of the foil to roll inward toward its center line, thus allowing light to pass into the camera. Experiments have shown that the shutter is 75 percent open in about 60 -- 80 microseconds. The shutter aperture may be made larger or smaller by changing the foil area and adjusting the electrical energy input to the foil.

Besides the well-known hydrogen line at 21 cm wavelength, the spectra of extraterrestrial radio sources may contain sharp lines characteristic of other atoms, ions, and small molecules. The detection and study of such line spectra would add considerably to present information on interstellar gas clouds and, perhaps, planetary atmospheres. Among the most likely producers of detectable radio line spectra are the light diatomic hydrides OH and CH; somewhat less likely sources are the heavier hydrides SH, SiH, and ScH. Very small concentrations of these hydrides should be detectable; in interstellar gas, concentrations as low as ** f molecules/** f may be sufficient, as compared to the ** f hydrogen atoms ** f required for detection of the 21 -- cm line.