Ferdinand II of Tuscany made the first sealed thermometer using wine spirit in 1641. This was the first device that we would recognise as a thermometer and was a major advance: a liquid sensor sealed against atmospheric pressure variations and evaporation, and degrees of temperature permanently marked on the stem. Subsequent developments of thermometers focused on improved methods of manufacture, especially on the choice of thermometric fluid and glass, and the method of fixing the scale.
By the early eighteenth century most liquid-in-glass thermometers were stable and had a reproducible scale. Typically the scales were marked using the temperatures of fixed points, such as melting snow, body temperature and boiling water (see Figure 1.3). The scale was then divided into a convenient number of steps or degrees. These scales are clearly ordinal scales with fixed points, and with the temperatures in between determined by interpolation using the expansion of the thermometric fluid, usually mercury. The familiar scales of Fahrenheit and Celsius are good examples of these types of scales. Elegant experiments involving the mixing of known volumes of hot and cold mercury, or hot and cold wine spirit, enabled experimenters to establish that mercury is a more linear thermometric fluid than spirit, but that both are non-linear to some extent.
In the late eighteenth century Gay-Lussac and Charles, building on the ingenious work of Amontons 100 years earlier, were both able to demonstrate that the thermal expansion coefficients of different gases were almost identical. Although Amontons had suggested that the linear expansion of gases with temperature implied that only one fixed point was required to calibrate a thermometer (i.e. to establish a metric scale), and a number of experiments determined values for absolute zero (−273.15 ° C), the sugges- tion was not adopted. Chappuis, working at the BIPM, refined gas thermometry further. He had been charged with the responsibility of calibrating a set of mercury-in-glass thermometers by gas thermometry. During a series of remarkable studies comparing temperatures determined using different gases he showed that the gas thermometer did in fact have a small gas species dependence, and that a scale based on hydrogen, although not ideal, was probably accurate to better than 0.01 °C. In 1889 the Confe´rence Ge´ne´rale des Poids et Mesures (CGPM), at its first meeting, adopted the first official temperature scale, the ‘normal hydrogen’ scale. Because of the known dependence of the scale on the non-ideal properties of hydrogen the initial filling pressure of the ther- mometer was also specified. This scale was still not a metric scale; instead the scale was defined by fixing the interval between the ice point and steam point to be 100 ° C. The scale was an ordinal approximation to an interval scale based on two fixed points and an almost linear interpolating instrument.
The first proposals to use the variation of electrical resistance to measure temperature came from Davy in 1821 and later Siemens in 1861. However, it took the elaborate experiments and refinements in the construction of platinum resistance thermometers by Callendar to get the resistance thermometer accepted. By comparing the platinum resistance thermometer with the gas thermometer, Callendar and others were able to show that platinum has a parabolic or quadratic characteristic. In 1899 Callendar proposed a temperature scale that would be more practical than the ‘normal hydrogen’ scale, based on three fixed points: the ice point, the steam point and the melting point of sulphur. The scale was defined by fixing the interval between the ice point and steam point to be 100 ° C, with the sulphur point defined to be 444.5 °C as determined by a gas thermometer calibrated at the other two points. Callendar’s proposal, again an ordinal
Ferdinand II of Tuscany made the first sealed thermometer using wine spirit in 1641. This was the first device that we would recognise as a thermometer and was a major advance: a liquid sensor sealed against atmospheric pressure variations and evaporation, and degrees of temperature permanently marked on the stem. Subsequent developments of thermometers focused on improved methods of manufacture, especially on the choice of thermometric fluid and glass, and the method of fixing the scale.By the early eighteenth century most liquid-in-glass thermometers were stable and had a reproducible scale. Typically the scales were marked using the temperatures of fixed points, such as melting snow, body temperature and boiling water (see Figure 1.3). The scale was then divided into a convenient number of steps or degrees. These scales are clearly ordinal scales with fixed points, and with the temperatures in between determined by interpolation using the expansion of the thermometric fluid, usually mercury. The familiar scales of Fahrenheit and Celsius are good examples of these types of scales. Elegant experiments involving the mixing of known volumes of hot and cold mercury, or hot and cold wine spirit, enabled experimenters to establish that mercury is a more linear thermometric fluid than spirit, but that both are non-linear to some extent.In the late eighteenth century Gay-Lussac and Charles, building on the ingenious work of Amontons 100 years earlier, were both able to demonstrate that the thermal expansion coefficients of different gases were almost identical. Although Amontons had suggested that the linear expansion of gases with temperature implied that only one fixed point was required to calibrate a thermometer (i.e. to establish a metric scale), and a number of experiments determined values for absolute zero (−273.15 ° C), the sugges- tion was not adopted. Chappuis, working at the BIPM, refined gas thermometry further. He had been charged with the responsibility of calibrating a set of mercury-in-glass thermometers by gas thermometry. During a series of remarkable studies comparing temperatures determined using different gases he showed that the gas thermometer did in fact have a small gas species dependence, and that a scale based on hydrogen, although not ideal, was probably accurate to better than 0.01 °C. In 1889 the Confe´rence Ge´ne´rale des Poids et Mesures (CGPM), at its first meeting, adopted the first official temperature scale, the ‘normal hydrogen’ scale. Because of the known dependence of the scale on the non-ideal properties of hydrogen the initial filling pressure of the ther- mometer was also specified. This scale was still not a metric scale; instead the scale was defined by fixing the interval between the ice point and steam point to be 100 ° C. The scale was an ordinal approximation to an interval scale based on two fixed points and an almost linear interpolating instrument.The first proposals to use the variation of electrical resistance to measure temperature came from Davy in 1821 and later Siemens in 1861. However, it took the elaborate experiments and refinements in the construction of platinum resistance thermometers by Callendar to get the resistance thermometer accepted. By comparing the platinum resistance thermometer with the gas thermometer, Callendar and others were able to show that platinum has a parabolic or quadratic characteristic. In 1899 Callendar proposed a temperature scale that would be more practical than the ‘normal hydrogen’ scale, based on three fixed points: the ice point, the steam point and the melting point of sulphur. The scale was defined by fixing the interval between the ice point and steam point to be 100 ° C, with the sulphur point defined to be 444.5 °C as determined by a gas thermometer calibrated at the other two points. Callendar’s proposal, again an ordinal
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