When was the mercury thermometer invented?
Mercury-in-glass thermometer
The mercury-in-glass or mercury thermometer was invented by physicist Daniel Gabriel Fahrenheit in Amsterdam (1714). It consists of a bulb containing mercury attached to a glass tube of narrow diameter; the volume of mercury in the tube is much less than the volume in the bulb. The volume of mercury changes slightly with temperature; the small change in volume drives the narrow mercury column a relatively long way up the tube. The space above the mercury may be filled with nitrogen gas or it may be at less than atmospheric pressure, a partial vacuum.
Hermann Fol
Fol is credited with the invention of the barthometer. The barometer properly measured mercury, the pressure to which the apparatus had been submitted, and the determination of the depth of compressible liquid within the device. His invention consisted of a spherical glass reservoir of a liquid that is slightly compressible, such as water or ether. The single hole to the vessel is a capillary tube that corresponds with a minor reservoir filled with mercury. Mercury, along the assumed temperature of the water at the sea bottom, must remain at the stage with the hole in the pointed stopper within the large reservoir. The top surface of the mercury is released to contact the water. The device is lowered by the sound line. The water or ether will compress as the device lowers, a given amount of each atmosphere of pressure, and a correlating amount of mercury will release between the hole and lower to the base of the bottom reservoir.