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Simultaneous measurements of atmospheric temperature fluctuations at various altitudes and locations at Mount Wilson Observatory provide a quantitative description of local turbulence characteristics. The average rms value of the temperature fluctuations at an altitude of 150 feet is found to be 26% of the rms value at 9 feet, showing a substantial decrease with altitude for temperature fluctuations close to the ground. These rms values are found to be more heavily dependent on wind speed than on time of night, in contrast to prior belief. For measurements made close to the ground, the power spectra of the temperature fluctuations closely fit the Kolmogorov-Taylor prediction of -1.67 at frequencies up to 8 Hz, although at higher elevations some discrepancy is observed: the mean slope at 70 feet is approximately -1.50. The average size of major turbulent eddies is found to depend on wind speed, varying approximately linearly from about 1 to 25 m in both the horizontal and vertical directions for wind speeds between 0 and 8 m s-1. Analysis of the correlation between horizontally separated sensors indicates that Taylor's approximation remains useful on timescales of 10-15 s, after which time the turbulence changes. This suggests that local measurements of temperature fluctuations could provide some appreciable correction to variations in path length in interferometric observations of stars caused by atmospheric turbulence.

The far-infrared rotational spectrum of H_2^16O has been studied in the spectral range 25–112 cm^−1 to measure the foreign-gas collision-broadened linewidths. Measurements of 17 lines broadened by nitrogen and 21 lines broadened by oxygen are reported. The measurements were made at 297 K. From these data, the widths due to air broadening are obtained. The experimental results are compared with recent theoretical calculations and with the case of a constant linewidth, equal to the average experimental width. There is some correlation between the relative experimental linewidths and the theoretical predictions. However, the simple assumption of a constant value for the collision-broadened linewidths gives a better representation for the case of N_2- and O_2-broadened linewidths than do present detailed theoretical calculations.

The combination of low atmospheric water vapor, high altitude, and low temperatures makes the South Pole and other high interior parts of the Antarctic continent particularly suitable locations for certain types of infrared or millimeter-wave astronomy. Information available on the atmospheric column density of water at the South Pole and at Vostok, the Soviet station, are surveyed. To illustrate the usefulness of these areas for infrared astronomy, important astronomical lines in the wavelength region 50 to 200 microns are listed. The atmospheric transmission in this wavelength region is also calculated and plotted for 0.1 mm and 0.3 mm of precipitable water along the line of sight through the atmosphere. Such low values of precipitable water occur frequently enough to allow practical astronomical observations from the ground and, for certain cases, this can provide advantages over observations from high-flying aircraft or satellites.

The effect of atmospheric fluctuations on measurements of distance has become increasingly important as laser interferometers become more widely used. The present study evaluates the precision with which dimensions can be monitored by interferometry involving optical path lengths in the open air under good atmospheric conditions. The size and time scale of optical path length fluctuations over distances of one meter, and correlations between fluctuations in nearby optical paths, are measured and analyzed.

The techniques of quantum electronics allow interesting new ways to generate and explore most of the acoustic spectrum and much of the electromagnetic domain. We can look forward to another decade of rapid development in this field From the time when man first saw the sunlight until very recently, the light which he has used has come predominantly from spontaneous emission, like the random emission of incandescent sources. So have most other types of electromagnetic radiation — infrared, ultraviolet, or gamma rays. The maximum radiation intensities, or specifically the power radiated per unit area per unit solid angle per unit frequency bandwidth, have been controlled by Planck's black-body law for radiation from hot objects. This sets an upper limit on radiation intensity — a limit which increases with increasing temperature, but we have had available temperatures of only a few tens of thousands or possibly a few millions of degrees.

Dans ce texte, Charles Hard Townes, inventeur du maser et père du laser optique, présente ses souvenirs de cette épopée.

WHERE the stars listed by Cocconi and Morrison are referred to in our article, 10 light years was erroneously written for 15 light years as noted by Dr. van de Kamp. Even this is not strictly correct, since one of the distances is as large as 16.5 light years. But these differences are not crucial for our purposes.