PERRET OPTICIANS INSTRUMENTS METEOROLOGY THERMOMETERS

Thermometers measure temperature. They may be fitted with a glass tube containing mercury or alcohol (The Thermometers with ‘alcohol ‘ have the toluol or the creosote as liquid, The alcohol is boiling at 78°C; this do not allow to measure temperature above 78°C) . Bimetal thermometers have a helicoidally spring. The two metals react differently to temperature, winding the spring to a lesser or greater degree. Electric resistance depends on temperature.

The glass balls are floating in a liquid. Due to changes in temperature the balls rise or fall in the liquid. The engraved metal temperature indication on the engraved plate indicates a lower weight of the plate. The actual temperature is shown by the lowest floating ball in the upper part of the thermometer.

LIQUID THERMOMETER

Manufactured after the idea of Galileo Galilei (1564-1642)

History

Searching for exact temperature measurements the brilliant Galileo Galilei discovered this fascinating method: Galilei put 4-5 exactly weighted balls in a cylinder filled with a special liquid. The balls goes up or down according to the existing temperature. By this method you can determine the correct temperature.

Temperature indication

In liquid, a solid body with the same weight and size ist compelled to go down as the temperature rises. On the other hand the solid body goes up in the liquid if the temperature falls. The glass bails differ in weight and considering the density of the liquid you are Guaranteed that the lowest of the floating balls in the upper part of the cylinder indicates the right temperature.

Manufacture

The production of this instrument ist extremely complicated and only able through handwork. Each ball ist glass-blown and calibrated to exactly 1/10 ° C. Two Glass balls differ in weight by only three thousands of a Gram. Due to the excellent workmanship, the measurement accuracy is to within 1/2°C.
Because of its accuracy and exclusiveness we are convinced that you will not regret having bought this instrument.

The liquid in the cylinder is free of CF2 gases, almost inflammable and neither poisonous nor does is cause any vapor or gas injurious to health.

Anders Celsius, born in Uppsala, was one of a large number of scientists (all related) originating from Ovanåker in the province of Hälsingland. The family name is a latinised version of the name of the vicarage (Högen). His grandfathers were both professors in Uppsala: Magnus Celsius the mathematician and Anders Spole the astronomer. His father, Nils Celsius, was also professor in astronomy. Celsius, who was said to have been very talented in mathematics from an early age, was appointed professor of astronomy in 1730.

For his metereological observations he constructed his world famous Celsius thermometer, with 0 for the boiling point of water and 100 for the freezing point. After his death in 1744 the scale was reversed to its present form.

Fahrenheit's parents both died in 1701 when he was 15. His guardian then sent him to Amsterdam to study business. The young Fahrenheit became fascinated with scientific instruments. He bounced around Europe, learning from scientists and craftsmen in different cities. In his wanderings, he met Olaus Roemer, a Danish astronomer, in Copenhagen.

Though thermometers had existed for more than a century, Roemer developed one very similar to the one we use today. Instead of mercury, Roemer used alcohol, in the form of wine, as the inner liquid that responded to temperature changes. Roemer's thermometer had two reference points: he chose 60 degrees as the temperature of boiling water and 7 1/2 degrees as the temperature of melting ice.

Fahrenheit, no fan of "inconvenient and awkward fractions," according to his letters, modified Roemer's scale. He divided each degree into four parts and used mercury rather than wine.

Fahrenheit established three fixed points on his thermometer. Zero degrees was the temperature of an ice, water, and salt mixture. When he omitted salt from the slurry, he reached his second fixed point when the water-ice combination stabilized at "the thirty-second degree." His third fixed point was "found as the ninety-sixth degree, and the spirit expands to this degree when the thermometer is held in the mouth or under the armpit of a living man in good health."

After Fahrenheit died in 1736, scientists calibrated his model of thermometer using 212 degrees, the temperature at which water boils, as the upper fixed point. When the Fahrenheit thermometer was recalibrated, normal human body temperature registered 98.6 rather than 96.

This post-Fahrenheit version of the Fahrenheit scale is now used in most English-speaking countries

Réaumur, René Antoine Ferchault de , 1683–1757, French physicist and naturalist. He invented an alcohol thermometer (1731) and the Réaumur temperature scale, in which the freezing point of water is 0° and the boiling point 80°.

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