In Sickness and In Health

Body temperature and its measurement

What makes your blood boil? Why are some people hot headed and others cold hearted? These, of course, are metaphors, but the mechanisms controlling body temperature are vital to our existence.

Temperature measurement

A new display at the University of Sydney’s Macleay Museum explores the history of ideas about body temperature. In Sickness and In Health: Body temperature and its measurement examines the interconnected history of ideas about body temperature and the development of thermometers. With modern infrared technology the different temperatures of different parts of the body can be displayed with artificially coloured images. The display includes a magnificent thermal image of a pregnant woman. Localised raised temperatures can also indicate maladies and injuries. There is evidence that the ancient Egyptians some four thousand years ago noted raised temperatures in relation to sickness, and no doubt this correlation had been observed long before.

The development of thermometers from the seventeenth century onwards enabled the concept of temperature to be standardised. At the very end of the sixteenth century Galileo developed the forerunner of the thermometer. He called it a thermoscope. (Fig. 1) This showed the rise and fall of air temperature but it had no scale and so no specific temperatures could be stated. The first real thermometer – a tube graduated with a scale – was developed about 1620 by Santorio who was specifically interested in applying quantitative techniques to human physiology.

An experimental society in seventeenth century Florence, the Accademia del Cimento, developed a variety of thermometers. (Fig. 2) These were enclosed and therefore not affected by changes in atmospheric pressure. Some of these were very long, allowing for the great expansion of alcohol over relatively small temperature ranges. Among the most impressive Florentine thermometers were the spiral versions in which the tubes were formed into a spiral in order to make them compact. The display includes a photograph of a surviving example of a spiral thermometer preserved in Florence and another photograph of a ‘frog’ thermometer in Florence. These thermometers – shaped like a frog – were specifically for taking a person’s temperature, being strapped to the arm. They were called infingardi (lazy) because they responded very slowly – no good in a medical emergency!

These early thermometers were all individual. There was no standardised scale of temperatures, and even two thermometers of the same type were only approximately equivalent. The eighteenth century saw the development of a number of temperature scales, including those of Fahrenheit and Celsius which still used today. In 1724 Daniel Gabriel Fahrenheit invented the Fahrenheit scale based on two fixed points. He marked the temperature of water mixed with ice and sea salt as 0 degrees and healthy body temperature as 96 degrees. Some years later, in 1742, Anders Celsius proposed a ‘centigrade’ scale, that is a scale of 100 degrees between two fixed points. He designated the boiling point of water as 0 degrees and the melting point of ice as 100 degrees. This upside-down scale seems odd today, but it had the advantage, especially to Celsius in his native Sweden, that colder temperatures remained positive and so daily life was not a mixture of positive and negative numbers. Subsequently the scale was reversed to produce the Celsius scale we know today.

In Sickness and In Health incorporates a variety of thermometers including an impressive early nineteenth century wall thermometer by W. & S. Jones of London, on loan from the Powerhouse Museum, and a late nineteenth century clinical thermometer, on loan from the Royal Australasian College of Physicians.

In Sickness and In Health: Body temperature and its measurement was developed by Fiona Mackenzie and Krista Sigurdson, honours students in History and Philosophy of Science at the University of Sydney. The display was launched by Professor Beryl Hesketh, Dean of the Faculty of Science, on Tuesday 27 November, the 300th anniversary of the birth of Anders Celsius. In Sickness and In Health was sponsored by the National Association of Testing Authorities, Australia (NATA) and will run until May 2003.