The word thermometer is derived from the Greek words thermo meaning warm and meter meaning measure. The thermometer was first invented by Galileo. It consisted of a series of glass spheres filled with varying densities of alcohol which would rise and fall in a closed tube of water depending on temperatures. From this another invention was made around the same time in the sixteenth or seventieth century which was known as the air thermometer. The open end of a closed tube was submerged in water any change in the air temperature would cause the water in the tube to rise or fall. The first modern thermometer was invented containing alcohol and completely closed ends by Grand Duke of Tuscany de' Medici. The thermometer at that time would take approximately 20 minutes to read. Later on in 1866 Sir Thomas Albutt introduced the clinical thermometer that would read the temperature in 5 minutes. The Mercury thermometer was invented by a German physicist Daniel Fahrenheit. The thermometer is usually kept under the arm, in the mouth. The silver tip and the line inside the glass tube consist of mercury.
Mercury is one of the few metals that are liquid at room temperature. It linearly expands as temperature increases. Another reason for mercury to be used in a thermometer is because it remains in a liquid state up to 300 degrees Celsius. This is why it can is used to measure body temperature. Also it is a shining metal and is easily seen which makes it easy to read the temperature. Mercury does not wet the glass of the thermometer and thus makes the thread move up and down without breaking. The mercury expands depending on the heat given to it. However the use of mercury thermometers is diminishing as many countries have banned them outright from medical use as a person by chance could swallow this or if broken could cause harm. It is rightly said that 1 gram of mercury present in a thermometer is enough to contaminate all the fish in a 20 acre lake. Chronic exposure to mercury could cause damage to the brain, spinal cord, kidneys, liver and even the fetus. In case the thermometer does break you just need to open the windows and not clean it up as it will be absorbed by your skin which is dangerous. Now days it is more advisable to use a digital thermometer rather than a mercury one.
Submitted by M T on January 14, 2010 at 08:17