Mercury-in-glass thermometer the thermometer, the bulb is made to reach thermal equilibrium with a temperature standard such as an ice/water mixture, and then with another standard such as water/vapour, and the tube is divided into regular intervals between the fixed points. In principle, thermometers made of different material (e.g., coloured alcohol thermometers) might be expected to give different intermediate readings due to different expansion properties; in practice the substances used are chosen to have reasonably linear expansion characteristics as a function of true thermodynamic temperature, and so give similar results. The application of mercury (1714) and Fahrenheit scale (1724) for liquid-in-glass thermometers
Medical thermometer non-linearity, and unsuitability for use in extreme temperatures Some electronic thermometers may work by contact (the electronic sensor is placed in the location where temperature is to be measured, and left long enough to reach equilibrium). These typically reach equilibrium faster than mercury thermometers; the thermometer may beep when equilibrium has been reached, or the time may be specified in the manufacturer's documentation. Other electronic thermometers work by remote sensing: an infrared sensor responds to the radiation spectrum emitted from the location. Although these are not in direct contact with the area being measured, they may still contact part of