Techniques are described for constructing cavity resonators at X band from low-thermal expansion ceramics. A variety of mechanical arrangements is discussed. Q values as high as 14 000 and frequency-temperature coefficients as low as 1 part in 100 million per °C have been obtained using simple processes.

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In recent years various instruments and techniques have been developed for measuring distances electronically. The accuracy of such measurements depends on the accuracy with which time and the velocity of propagation of radio waves can be determined. The National Bureau of Standards, under the sponsorship of the Air Force Ballistic Missile Division, has been studying the effects of atmospheric turbulence on the performance of radio distance‐ and/or velocity‐measuring systems. Many of the data collected in this study are applicable to the problem of determining the accuracy of radio surveying methods, Longterm variations in the apparent length of a 15.5‐mile path in Hawaii are shown, along with the effects of correcting for the atmospheric refractive index observed at 2 to 5 points along the path.

These include the development and maintenance ol the national standards of measurement and the provision of means and methods for making measurements consistent with these standards: the determination of physical constants and properties of materials; the development of methods and instruments for testing materials, devices, and structures; advisory services to Government Agencies on scientific and technical problems; invention and development of devices to serve special needs of the Govern¬ ment; and the development of standard practices, codes and specifications. The work includes basic and applied research, development, engineering, instrumentation, testing, evaluation, calibration services, and various consultation and information services.A major portion of the Bureau's work is performed for other Government Agencies, par¬ ticularly the Department of Defense and the Atomic Energy Commission. The scope of activities is suggested by the listing of divisions and sections on the inside back cover.

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