Table of contents

Visually, this issue of Metrologia differs markedly from those of recent years. The cover is changed and the layout of articles is not quite what it was before. Older readers, however, may notice that the colour of our new cover is that used for the original eleven volumes published in the period 1965-1975. The choice is deliberate: this combination of innovation with a respect for older forms characterizes the way Metrologia will operate under its new publisher the Bureau International des Poids et Mesures.

In discussion of the new Metrologia, one decision was firm: our underlying editorial policy remains fixed. Metrologia will remain a primary vehicle through which the metrological community communicates progress in fundamental scientific measurements, reports original experiments and techniques, reviews work in specialist fields and disseminates the decisions of the Comité International des Poids et Mesures.

This year, we plan six issues. Four will be regular research issues, one, appearing mid-Summer, will record the proceedings of the meeting held in Davos, Switzerland 20-22 September 1990 on "New Developments and Advances in Optical Radiometry III" and another, towards the end of the year, will review progress in Nanometrology. If successful, the pattern will be repeated, the intention being that the research issues continue Metrologia's historical line of interest, the conference issues expose the journal to new authors and the review issues realize a long-standing, but largely inactive, objective of editorial policy, the provision of retrospective evaluations of important topics and the assessment of likely developments in selected aspects of metrology.

The International Temperature Scale of 1990, ITS-90, came into effect on 1 January 1990, replacing the International Practical Temperature Scale of 1968, IPTS-68, and the "Echelle Provisoire de Température de 1976 entre 0,5 K et 30 K", EPT-76. The present paper reviews the various experimental measurements of thermodynamic temperature T (often expressed as differences (T - T₆₈)) in the range 0,65 K to 1 357,77 K, which were available prior to September 1989, and on the basis of which values of temperature were adopted in the ITS-90. Estimates are given for the uncertainties in the derivation of these values.

An international comparison has been made of the frequencies of stabilized He-Ne lasers using intracavity saturated absorption of ¹²⁷I₂ at λ = 633 nm in Bratislava (Czechoslovakia).

This comparison, organized by the CSMU (Bratislava), involved at the same time seven laboratories from five countries: the ASMW (German Democratic Republic), the CSMU (Bratislava, Czechoslovakia), the CSMU (Praha, Czechoslovakia), the CSAV (Brno, Czechoslovakia), the OMH (Hungary), the VNIIM (USSR) and the BIPM.

The range of the frequency differences between all the lasers and the two BIPM travelling lasers was from - 15,9 kHz to 8,8 kHz, with a mean of Δf = - 3,3 kHz and an estimated standard deviation of 8,5 kHz (4,7 kHz corresponds to 1 part in 10¹¹, in relative terms).

Using the measurements carried out at the BIPM before and after this comparison between the travelling lasers BIPM4 and BIPM10 and the stationnary reference laser BIPM2, we can link our results to previous international comparisons involving the BIPM. Taking into account the values of these measurements, the mean frequency difference becomes: Δf = - [1,6 ± 8,2] kHz.

Interferometric dilatometers at the National Research Laboratory of Metrology (NRLM) in Japan and the National Physical Laboratory (NPL) in UK been intercompared by measuring the thermal expansion coefficients of pure polycrystalline silicon, a low expansion ceramic (Miraclon) and fused silica (SRM 739). The dilatometers, two from each laboratory, were intercompared over their respective operating temperature ranges of 250 to 375 K and 290 to 800 K. The results presented in this paper show that the agreement for each material is within the combined uncertainties in the measurement of each thermal coefficient of expansion.

A measurement of the thermal dilatation of pure water has been made by detecting the change of buoyancy acting on a cylindrical hollow artifact made of fused quartz immersed in water between the temperatures of 0 °C and 44 °C. The formula for the thermal dilatation of water, free from air, is obtained in terms of the relative density ρ/ρ₀ at the pressure of 101 325 Pa with an uncertainty of less than 1 ppm is as follows:

ρ/ρ₀ = 0,999 867 75 + 6,786 687 54 × 10^-5(t/°C) - 9,090 991 73 × 10^-6(t/°C)² + 1,025 981 51 × 10^-7(t/°C)³ - 1,350 290 42 × 10^-9(t/°C)⁴ + 1,326 743 92 × 10^-11(t/°C)⁵ - 6,461 418 × 10^-14(t/°C)⁶

where the temperature of the maximum density ρ₀ is 3,983 4 °C in terms of the ITS-90. The uncertainty of the measurement and the derived formula is evaluated to be 0,2 to 0,5 ppm in standard deviation for the same temperature range.

The density of ambient air has been determined by a straightforward experimental method. The apparent masses of two artefacts having about the same mass and surface, but different well-known volumes, have been compared by using a 1 kg balance in vacuum and in air. The differences of apparent masses and volumes yield the air density with a relative uncertainty (1σ) of 5 × 10^-5. From measurements made using a third artefact, surface sorption effects caused by the change between vacuum and air conditions gave a coefficient of about 0,2 μg cm^-2.

A comparison is reported of a deadweight pressure tester using gas lubrication and the liquidfilled primary pressure State standard, accepted in the Soviet Union. The comparison is within the pressure range of 0,02 to 4,0 kPa. The standard error of the tester was shown to vary within the range 0,08 to 0,30 Pa. This portable tester 300 × 190 × 290 mm is intended as a secondary, transfer, standard.