RAIN gauge, a machine for measuring the quantity of rain that falls. There are various kinds of rain-gauges : that used at the apartments belonging to the Royal Society at Somerset- muse, is thus de scribed. The vessel which receives the rain is a conical funnel, strengthened at the top by a brass ring twelve inches in diameter. The sides of the funnel, and inner lip of the brass ring, are inclined to the horizon in an angle of more than 65°, and the outer lip is an angle of more than 50., which are such degrees of steepness, that there seems no probability either that any rain which falls within the funnel, or on the inner lip of the ring, shall dash out, or that which falls on the outer lip shall dash into the funnel.
Plate XIII. Misc. fig. 9, represents one of the best constructiorr of rain-gauges. It consists of a hollow cylinder, having within it a cork-ball attached to is wooden stem, which passes through a small open ing at the top, on which is placed a large funnel. When this instrument is placed in the open air in a free place, the rain that falls within the circumference of the funnel will run down into the tube, and cause the cork to float ; and the quantity of water in the tithe may be seen by the height to which the stem of the float is raised. The stem of the float is so gra
duated, as to show by its divisions the number of perpendicular of water which fell on the surface of the earth since the last observation. It is hardly necessary to observe, that after every observation the cylinder must be emp tied.
A very simple rain-gauge, and one which will answer all practical purposes, consists of a copper funnel, the area of whose opening is exactly ten square inch es : this funnel is fixed in a bottle, and the quantity of rain caught is ascertained by multiplying the weight in ounces by .173, which gives the depth in inches and parts of an inch. In fixing these gauges, care must be taken that the rain may have free access to them : hence the tops of buildings are usually the best places. When the quantities of rain collected in them at different places are compared, the instruments ought to be fixed at the same heights above the ground at both places, because, at different heights, the quantities are always different, even at the same place.