Consequently, even measurements made with instruments produced by the same maker were not guaranteed to be comparable.
Two strategies were pursued to overcome this state of affairs: calibrating instruments against some standard reference instrument and constructing fixed-point-scales from first principles. The former approach was undertaken by the Academia del Cimento around 1654 and the Royal Society of London about 1665. Distribution of their instruments made possible the first intelligible meteorological temperature records, but intercomparison with instruments not calibrated to their standards was difficult if not impossible. The latter approach was pursued with scales having either one or two fixed points. Robert Hooke (1635-1702) constructed a scale using one fixed-point and having degrees correspond to equal increments of the thermometricsubstance volume. Scales with two fixed points had their degree markings defined as some fraction of the distance between the fixed points. Carlo Rinaldini (1615-1698) first suggested the melting point of ice and boiling point of water as appropriate fixed points. He divided his scale into twelve degrees (1694).
Though much progress was made, confusion was still the order of the day. Because volume is that property of substances which is most readily perceived to change with temperature, it was the preferred means of measuring temperature in early thermometers.
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