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 or it may be at less than
atmospheric pressure, a partial
vacuum.