The measurement of temperature is a comparatively new concept. Early scientists understood the difference between ãhotä and ãcold,ä but they had no method to quantify varying degrees of heat until the seventeenth century. In 1597, Italian astronomer Galileo Galilei invented a simple water thermoscope, a device that consisted of a long glass tube inverted in a sealed jar that containing both air and water. When the jar was heated, the air expanded and pushed the liquid up the tube. The water level in the tube could be compared at different temperatures to show relative changes as heat was added or removed. However, the thermoscope lacked an easy way to directly quantify temperature.

Several years later, the Italian physician and inventor Santorio Santorio improved Galileoâs design by adding a numerical scale to the thermoscope. These early thermoscopes led to the development of the fluid filled thermometers commonly used today. Modern thermometers operate based on the tendency of some fluids to expand when heated. As the fluid inside a thermometer absorbs heat, it expands, occupying a greater volume and forcing the fluid level inside the tube to rise. When the fluid is cooled, it contracts, occupying a smaller volume and causing the fluid level to fall.

Temperature is a measure of the amount of heat energy possessed by an object. Because temperature is a relative measurement, scales based on reference points must be used to accurately measure temperature. There are three main scales commonly used in the world today to measure temperature: the Fahrenheit (*F) scale, the Celsius (*C) scale and Kelvin (K) scale. But there are some other scales which is obsolete: the Reaumur (*Reaumur) scale, the Rankine (*Rankine) scale, the Newton scale, the Romer scale, the Delisle scale, the Leyden scale. Each of these scales uses a different set of divisions based on different reference points.