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Synopsis The accuracy of some setting methods applicable in two-beam interferometry is investigated with regard to its dependence on the conditions of observation. Photometric methods prove to be the most advantageous. With these, an accuracy of a few thousandths of a wavelength in one setting is attainable under favourable conditions.

Water vapor in the atmosphere of Venus was discovered in November 1959 by observations made at 80000-ft. altitude with a manned balloon-telescope system. This result was confirmed and measured far more precisely in February 1964 with an automatic unmanned system. The method of observing Venus water-vapor absorption in the 1.13-μ band, and the interpretation of that absorption, are described.

Temperature quenching causes a marked increase of the rate of decay of fluorescence. It is shown that both the efficiency of fluorescence and the decay are determined by the probabilities of the fluorescence transition and of a radiationless transition. By combining data from measurements of the efficiency and the decay, it is possible to obtain the two transition probabilities separately, and both as a function of the temperature. The results with (NH 4 ) 3 UO 2 F 5 and Mg 2 TiO 4 . Mn 4+ have been used to verify whether the radiationless process follows the theory of Mott and Seitz, or of Moglich and Rompe; they are found to favour the former.

Descriptions of a SISAM-interferometer for space application and of the performance of a Michelson type Fourier transform interferometer are given. The benefits and disadvantages of both instruments in different applications are discussed. The usable wavelength range for the SISAM ranges from 1 to 9 μ (extensible up to 100 μ). The Michelson interferometer is designed for the far infrared beyond 25 μ. The obtained spectral resolution is 0.2 cm−1 and 1 cm−1 respectively. Atmospheric effects on high resolution measurements from balloon or aircraft are discussed.

The interferometer consists of a beamsplitter and two spherical mirrors. Each mirror forms an image of the source on the detector. The transfer function is calculated for a point source and various detectors comparable in size to the diffraction images. The path difference is introduced by moving either one or both of the mirrors. For large detectors, the maximum-permitted path difference is twice the focal tolerance. For small detectors, the usable path difference is somewhat larger but depends on the manner in which the path difference is varied.

Far UV spectral intensity of B3 V star from Aerobee rocket scanning prism spectrometry, noting discrepancy with model atmosphere predictions