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.
A hygrometer is a tool used to measure the moisture content of the air. It can be used either indoors or outdoors, but devices are usually specifically for one or the other. The hygrometer is very specialized and only gathers data about moisture content.