How did people determine body temperature before thermometers were invented?

Humans have been looking for ways to measure temperature since a long time ago. Although people did not have the concept of "temperature" at that time, they would use the feeling of the body to define the change of hot and cold. Today, after more than 400 years of development, the thermometer is no longer limited to measuring ambient temperature and body temperature, but provides accurate temperature data for all aspects of our life and production, and has formed a classified science - thermometry.

Today, let’s take a brief look at the history of thermometer development.

Perceive temperature changes based on experience - ice bottle, fire

In ancient times, people generally used body sensations to define changes in temperature. In addition, the ancients also discovered many ways to sense changes in the external environment temperature.

As early as the pre-Qin period, the ancients would use bottles filled with water to observe temperature changes. There is a saying in "Lüshi Chunqiu·Shen Dalan·Chajin": "Seeing the ice in the bottle of water, you can know how cold the world is and where the fish and turtles are hiding." It means that if you put water in a bottle and the water freezes, you can know that the temperature is very low and it is winter; if the ice melts, the temperature rises. This kind of bottle is called an "ice bottle" and can be said to be the most primitive thermometer in China. In the process of metal smelting or firing ceramics, craftsmen of all generations would use the color of the flame to judge the temperature in the furnace.

Principle: The ice bottle is a method used by the ancients to infer the changes in the temperature of the environment by using the changes in the shape of water at different temperatures, and the fire temperature is a high-temperature visual measurement technology created by the ancients. However, these are only empirical perceptions and cannot be accurately measured.

The world's first thermometer - Galileo thermometer

Before the invention of the thermometer, the only tool to understand the patient's temperature was the hand. At that time, medicine already knew that the patient's condition was related to the temperature of his body, but if the doctor happened to have a slight fever that day, or had just touched a relatively cool object, the result would be inaccurate. Therefore, Galileo wanted to invent a tool that could measure heat. In 1593, Galileo first applied the phenomenon of air expansion and contraction to the invention of the thermometer.

Principle: When the substance being measured (air) comes into contact with the glass bulb, the air above the glass tube will change in volume due to thermal expansion and contraction, causing the colored liquid column to rise or fall accordingly. By referring to the numbers marked on the glass tube, the specific temperature of the substance can be measured. This is the world's first scaled thermometer - the gas thermometer.

The main problem is that the volume of a gas is affected not only by temperature but also by atmospheric pressure. At that time, people did not know the existence of air pressure, so Galileo's thermometer was not accurate and had a large measurement error, but Galileo failed to solve this problem.

The first improvement: the snake-shaped thermometer was invented

In 1611, Galileo's student Sanctorius improved the first thermometer. Now it seems very strange. He changed the straight tube of the thermometer into a snake-shaped curved tube and reduced the volume of the glass bulb so that it could be stuffed into the patient's mouth. He also engraved about 110 scales on the curved glass tube to indicate the temperature change, which was used to measure body temperature. This is the world's earliest thermometer.

Principle: It is still the thermal expansion and contraction of air. Thinner and longer glass tubes can make the measurement more accurate, while bent tubes are more convenient to use and read.

The main problems were: it was still affected by atmospheric pressure, so the measurement was inaccurate; moreover, there was no unified standard for measuring temperature at that time.

Directions for improvement: Get rid of the influence of atmospheric pressure (replace gas with liquid), be smaller and more convenient to carry.

The first liquid thermometer - the change from water to alcohol

In 1650, Ferdinand of Italy first chose water as a liquid thermometer, but there were two problems: first, the melting and boiling points of water determine that the measurement range of a thermometer made of water is relatively small (0~100℃); second, water has a special property, that is, its density is the largest and its volume is the smallest at 4℃, which means that water has a "reverse expansion" phenomenon of shrinking when heated and expanding when cooled at 0~4℃. Therefore, measurements below 4℃ will be inaccurate and will even burst the glass shell.

Ferdinand tried a variety of liquids and finally chose alcohol, which is easy to obtain. This is because alcohol has a much lower freezing point and a very obvious thermal expansion and contraction phenomenon. However, the alcohol thermometer also has problems: the boiling point of alcohol is 78°C and the freezing point is -117°C (the measuring range is -117~78°C). Therefore, although the alcohol thermometer can be used at low temperatures, it cannot measure the temperature of objects above 78°C, such as boiling water.

Principle: Liquids expand when heated and contract when cooled.

The main problem: the measuring range is not large enough.

Direction for improvement: Use liquids with higher boiling points and more obvious thermal expansion and contraction.

The first mercury thermometer - the prototype of the modern thermometer

In 1659, French astronomer Brioli used the high boiling point of mercury to create the first mercury thermometer with a measuring range of -39~357℃. This thermometer already had the prototype of the modern thermometer.

Principle: Liquids expand when heated and contract when cooled.

The main problems are: it has a certain measurement range, but the lower limit is relatively high, so it is not suitable for use in colder areas; mercury is volatile and toxic.

Modern temperature measurement technology - the great development of thermometers

With the development of science and technology, various thermometers emerge in an endless stream, providing various quality temperature values ​​for our daily production and life, such as thermocouple thermometers and infrared thermometers. All of this has slowly developed from the Galileo thermometer. I believe that in the future, there will be more types of thermometers to make our production and life more convenient.

Principle: Thermometers no longer rely on thermal expansion and contraction, but rather on changes in other quantities (such as resistance) caused by temperature changes, and then present changes in temperature values ​​through data processing.

Text/Wang Congcong Photo/Internet