THE SMITHSONIAN INSTITUTION. 



227 



witli a stantlard barometer, to ascertain whether it has undergone 

 any change. 



OMBROMETER. 



Placing. — The omhrometer, or rain-gage, is a funnel, accompanied 

 hy a graduated cylindrical glass vessel, and by a reservoir. It should 

 be placed in an open space. Trees, high buildings, and other ob- 

 stacles, if too near, may have a considerable influence in increasing 

 or diminishing the quantity of rain which falls into the funnel.^ The 

 surface of the'receiver should be placed horizontally about six inches 

 above the ground. The most simple mode of establishing it is the 

 following : 



Place in the ground a cask or barrel, (Fig. 9,) water-tight, the top 

 rising above the ground about three inches ; cover it with boards 

 slightly inclined in the form of a roof, which project on all sides 

 beyond the edge of the barrel at least a foot. A circular opening in 

 the middle receives the funnel, the borders of which rest on the board. 

 At the bottom of the barrel, to receive the water, is an earthen pr 

 metallic vessel, with a narrow neck, (an ordinary earthen jug will 

 answer,) in which is placed the end of the funnel, exactly filling the 

 opening. It must contain two or three quarts. The funnel is fastened 

 by means of two clasps to the board, which must be covered up with 

 sod, to make it like the ground itself. If circumstances render it 

 necessary to place the ombrometer higher, the height must be carefully 



*'l2. 9. 



noted in the journal. If it is placed upon a sloping roof, it should 

 be on the top, and not at the edges, or at the angles, and must be 

 raised several feet above the roof itself. 



Observation. — To make the observation, remove the funnel, and 

 pour the water from the jug into the large graduated glass cylinder. 

 The opening of the funnel being one hundred square inches, one inch 

 of rain in depth gives one hundred cubic inches of water ; and each 

 division of the glass containing a cubic inch of water, each of them 

 represents a hundredth of an inch of rain fallen into the ombrometer. 

 These degrees are large enough to permit us to estimate the thou- 



