THE ACTION OF THE RAIN-CORRECTING 

 ATMOMETER 



E. M. HARVEY 



University of Chicago, Chicago, Illinois 



Since the rain-correcting atmometer was described by Living- 

 ston' in 1910, a few of these instruments seem to have come into 

 use, but perhaps not so many as their accuracy and simplicity 

 should justify. A reason for hesitancy in making use of this 

 apparatus may be due to the fact that, though one might easily 

 work out by simple physical principles how the instrument ought 

 to act under various assumed conditions, yet no published account 

 has shown just how it does act when exposed to conditions as 

 found in the field. 



Considering this matter worthy of some attention, a set of 

 experiments were carried out to determine the answers to several 

 questions regarding the operation of the rain-correcting appa- 

 ratus. These questions may be stated somewhat as follows: (1) 

 Just how do the mercury valves behave under the influence of 

 different kinds of showers? (2) How great is the error involved 

 in the operation of the valves (i.e., to reverse them), and on what 

 does this error depend? (3) Is the absorption of rain by the 

 ordinary porous cup atmometer of sufficient amount to justify the 

 use of a rain-correcting device? 



Six Li\'ingston automatic rain-correctors were made and at- 

 tached to standard 2 atmometers. The glass tubes were of the 

 thick-walled and small-bore type, frequentlj^ termed barometer 

 tubing. The cups drew their water from burettes. A lead tube, 

 connected with a water supply, was placed above each cup so 



1 Livingston, B. E., A rain-correcting atmometer for ecological instrumentation. 

 Plant World 13: 79-82. 1910. 



2 Livingston, B. E., Operation of the porous cup atmometer. Plant World, 

 13: 111-118. 1910. See also Livingston, B. E., A rotating table for standardiz- 

 ing porous cup atmometers. Plant World, 13: 157-162. 1912. . 



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THE PLANT WORLD, VOL. 16, NO. 2, MARCH, 1913 



