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Measurements at 2.653 GHz of the dielectric properties of seawater samples collected over the world's oceans and NaCl solutions over the concentration range 0.3 N to 0.7 N have been made over the temperature range 5.5° to 24°C to an accuracy of 0.2% in the real part of ε and 0.4% in the imaginary part of ε. The measurements demonstrate that the dielectric properties of seawater can be determined from its chlorinity alone but are substantially different from those of the 3.35 wt % NaCl solution, which has been taken in all previous work as a model for seawater. The data are presented in a form that is well fitted by a linear dependence on chlorinity. The accuracy of the measurements removes the uncertainty in the dielectric properties of seawater as a significant source of error in S band radiometric determination of ocean surface temperature.

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Accurate measurements of collision-induced absorption in CO2 are made at a number of temperatures in the range from − 40 to 60°C in the wavelength region 7–250 cm−1. Direct evidence for the separation of the pure translational band from the rotational–translational band is obtained at all temperatures. This and other aspects of the band shape are discussed. Over the entire temperature range, the experimentally determined Kramers–Kronig integral is found to be in good agreement with the theoretical value, i.e., the static dielectric constant. This agreement is achieved only when the contribution of the quadrupole–quadrupole energy in the radial distribution function, of particular importance for CO2 because of its large quadrupole moment, is calculated accurately. A value of the quadrupole moment is obtained, (4.5 ± 0.2)10−26 esu, which is in satisfactory agreement with that obtained by the method of Buckingham and Disch, which does not depend on a knowledge of intermolecular force constants. Induction due to higher multipole moments and the overlap interaction is considered.

Coefficients of induced absorption in model atmospheres contaming CO2, N2, A, and Ne, needed to calculate the properties of the lower atmosphere of Venus from the radio observations on the assumption that the atmosphere is dry and massive, have been measured in the temperature range 240–500°K to pressures as high as 130 atm. Since the microwave region lies on the low‐frequency wing of both the translational and rotational spectrum, the microwave‐induced absorption coefficient is proportional to the square of the frequency, and all measurements have been made at one frequency, 9260 Mc/s. Absorption due to small amounts of water vapor in N2 has also been studied at 9260 Mc/s, over a comparable pressure range, and over the temperature interval 393–473°K. The absorption coefficient in this case is found to be approximately twice that calculated on the basis of the Van Vleck‐Weisskopf theory from all of the significant microwave and infrared transitions of the water molecule. An expression for the absorption coefficient for all the atmospheres studied that is faithful to the laboratory data to a few per cent over the range of pressures relevant to Venus is α = P2 2(273/T)5(15.7ƒ + 3.90ƒ ƒN2 + 2.64ƒ ƒA + 0.085ƒN22 + 1330·ƒH O) × 10−8 cm−1 where P is the pressure in atm, is the frequency in wave numbers, T is the Kelvin temperature, and ƒCO2, etc., are the various molar fractions. The term in ƒH2O strictly applies only when N2‐H2O collisions are the major source of pressure broadening of the H2O lines. When this expression is used to calculate the brightness temperature as a function of frequency for Venus, it is concluded that (a) water vapor can account for the microwave spectrum only if water is several orders of magnitude more abundant than the infrared studies suggest and that (b) if induced absorption in a CO2‐N2 atmosphere is responsible for the spectrum, if CO2 is a relatively minor constituent of the atmosphere, and if the lapse rate is close to the adiabatic, then the ground pressure must lie in the range 100–300 atm.

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Experimental methods for determining the high-temperature millimeter-wave dielectric properties of solids are described and the data obtained on a wide variety of polycrystalline ceramics are reviewed. In general, the observed increase in dielectric constants with temperature can be modeled with a macroscopic dielectric virial expansion and shown to be primarily caused by an increase in polarizability due to volume expansion. The room-temperature loss tangents in low-absorption ceramics are probably caused by impurity doping of the primary and secondary crystalline phases at grain junctions and along grain boundaries. The rapid increase in loss tangent at high temperatures commonly observed in polycrystalline ceramics is associated with softening of intergranular amorphous phases resulting in an increase in localized electrical conductivity.