Storia del termometro per le misure ambientali: dai termoscopi ai sensori elettronici

Temperature studies began at the end of the sixteenth century, but they took a turn when, with the affirmation of the Galilean method, the realization of instruments happened that allowed scientists to transform from qualitative to quantitative their researches. In meteorology, scholars thus had an objective means of assessing the thermal state of the atmosphere by giving a new meaning to their observations. The first instruments carried out were essentially qualitative such as the thermoscope of G. Galilei (1597) and those of S. Santorio (1611) which were also used in medicine. In the sphere of the Galilean school, alcohol-in-glass thermometers were designed with various thermometric scales up to the definitive version (1646) with a fifty-degree scale which was reproduced in numerous copies, for almost a century, spreading throughout Europe. These thermometers were used in the first network for meteorological observations (1654-1665). In 1688, E. Halley proposed to use mercury as a thermometric liquid to overcome some defects of the alcohol thermometers. In the first half of the eighteenth century, to put order among the numerous thermometric scales, some scales were proposed (Fahrenheit, Celsius) that had as fixed points those of freezing and boiling of distilled water, at standard pressure. After 1750, recording thermometers were built that could memorize only a few measured values (Cavendish, Six-Bellani), which were followed by devices capable of detecting the temperature trend "continuously". Between the eighteenth and nineteenth centuries "metallic thermometers" were proposed which took advantage of the variations in volume that a solid metal undergoes as the temperature changes. In the nineteenth century electrical recording and the use of telegraphs favored the development of thermometers, as well as other meteorological instruments and measurement systems, which began to be built according to internationally established standards. In the seventies of the twentieth century a change happened in the structure of the thermometers with the passage from electromechanical ones with analogical recording of data to electronic ones with digital recording.