Heat and temperature

Like so many aspects of the revolution which led to the birth of modern science, the origins of the scientific study of heat and temperature can be traced to the early years of the seventeenth century. The quantitative study of heat and temperature depended upon the development of instruments which could give a quantitative measure of concepts such as ‘the degree of hotness’. The first appearance of the word thermomètre occurred in 1624 in the volume Récréaction Mathématique by the French Jesuit Jean Leurechon. This was translated into English in 1633 by William Oughtred, under the title Of the Thermometer, or an Instrument to Measure the Degrees of Heat or Cold in Aire. The Oxford English Dictionary gives 1633 as the date of the first appearance of the word ‘thermometer’ in English literature.

There had been earlier descriptions of the use of the expansion of gases to measure ‘the degree of hotness’, by Galileo and others, but the first thermometers which resemble their modern counterparts were constructed in the 1640s to 1660s. Coloured alcohol within a glass bulb was used as the expanding substance and this liquid extended into the long stem of the thermometer, which was sealed off to prevent evaporative loss of the fluid. In 1701, Daniel Fahrenheit constructed an alcohol-in-glass thermometer in which the sealed tube was evacuated. Then, in 1714, he extended the temperature range of the thermometer by using mercury rather than fluids, such as alcohol, which boil at relatively low temperatures.