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.
(Physical Geography) a type of hygrometer consisting of two thermometers, one of which has a dry bulb and the other a bulb that is kept moist and ventilated. The difference between the readings of the thermometers gives an indication of atmospheric humidity. Also called: wet-and-dry-bulb thermometer.