Note:  Do not rely on this information. It is very old.

Rain Gauge

Rain-Gauge, an instrument for measuring rainfall, consisting generally of a circular funnel, of known diameter, which leads to a receiver. If the diameter be 4-G97 inches, each fluid ounce of rain collected represents one-tenth of an inch, since the area will be 17'33 square inches and a fluid ounce at ordinary temperature is 1'733 cubic inches. Glaisher's gauge, recommended by the Royal Meteorological Society, is a copper cylinder 8 inches across and 18 inches high, with the funnel about half-way down, so as to allow for snow. The mouth of the funnel should be one foot from the surface of the ground, as, from wind and other causes, the amount registered varies at different heights.