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A ROTATING TABLE FOR STANDARDIZING POROUS 



CUP ATMOMETERS 



BURTON EDWARD LIVINGSTON 



The Johns Hopkins University, Baltimore, Md. 



Since the efficiency of the porous cup atmometer 1 depends 

 largely on the standardizing of each cup before and after its use, 

 the method used in standardization is exceedingly important. 

 As heretofore described, the operation consists in determining the 

 relatives rates of water loss from the cups to be standardized and 

 from a standard evaporating surface. The method of standardiz- 

 ing to an open dish of water (Plant World 13:111, 1910) has proved 

 unsatisfactory and has been abandoned. The discussion of this 

 proposition will be deferred to a later date. The only standard 

 now available is either a porous clay cup or a paper cylinder 

 (Plant World 14: 281, 1911). In either case the relative rates of 

 water loss, under the same surroundings, must be determined 

 for several time periods. It has been our practice to arrange the 

 series of cups to be standardized (mounted on glass tubes in small- 

 mouthed bottles, wdiich are filled at reading to a file mark on the 

 neck) about 50 cm. apart on a clean floor or table, trusting that 

 the convection and other currents of the surrounding air would be 

 sensibly similar about the various instruments. 



Where operations are carried on in the open, there is no objection 

 to this method, which is still in use at the Desert Laboratory for 

 the hundreds of standardizations necessary there for each year's 



^he instrument was devised in its essentials by Babinet (Compt. rend 27: 

 529-30. 1848). It was independently devised by A. Mitscherlich (Landw. Ver- 

 suchsstat,60: 63, and 61: 320. 1904), and by the writer (Publ.50, Carnegie Institu- 

 tion, 1906). The literature of this form of atmometer is presented in Plant World 

 13: 111-118. 1910. On a modification of the instrument, see Transeau, E. N., A 

 Simple Vaporimeter, Bot. Gaz. 49 : 459-60. 1910. 



For later literature see: Plant World 14: 96-99. 1911; Bot. Gaz. 62: 417-438. 

 1911 ; Plant World 14: 281-289. 1911. 



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