The longitude (abbreviation: Long., Î», or lambda) of a point on the Earth's surface is the angle east or west from a reference meridian to another meridian that passes through that point. All meridians are halves of great ellipses (often improperly called great circles), which converge at the north and south poles.
Use the dual thermometers to calculate relative humidity. Fisher Scientific Mason's Hygrometer has one dry thermometer and one wet thermometer which provide temperature readings for determining the relative humidity.
There are two commonly used types of hygrometers: Mechanical hygrometer and wet and dry bulb psychrometer. Wet and Dry Bulb Psychrometer. This is the easiest way to measure humidity. This type of hygrometer is equipped with two mercury thermometers, where one has a wet bulb and the other has a dry bulb. Because of the evaporation of water on the wet bulb the temperature will drop and read a lower temperature than what is displayed on the dry bulb.