PRFXIPITATION 



73 



106. The rain gauge, as the illustration shows, is a cylindrical vessel with 

 a funnel-shaped receiver at the top, which is 8 inches in diameter. The re- 

 ceiver fits closely upon a narrower brass vessel or measuring tube in which 

 the rain collects. The ratio of surface between receiver and tube is lo to i. 

 For readings covering a general area, the rain-gauge is placed in the open, 

 away from buildings or other obstructions, and is sunken in the ground suffi- 

 ciently to keep it upright. In localities where winds are strong, it is usually 

 braced at the sides also or supported by a wooden frame. In measuring 

 the amount of rain in the measuring tube, the depth is divided by ten in 



Drant Tieu>. 



VertieaZ StcUoru 



Hartzantal Seetian.^9 



Rain gauge showing construction. 



order to ascertain the actual rainfall. The depth is measured by inserting 

 the measuring-rod through the hole in the funnel until it touches the bot- 

 tom. It is left for a second or so, quickly withdrawn, and the limit of the 

 wetted portion noted. In the case of standard rods, the actual rainfall is 

 read directly in hundredths, so that the division by ten is unnecessary. 

 After each reading, the measuring-tube is carefully drained, replaced, and 

 the receiver put in position. No regular time for making readings is neces- 

 sary. During a rainy period, it is customary to make a measurement each 

 day, but it has been found more satisfactory for ecological purposes to 

 measure each shower, and to record its duration. These two facts furnish 



