ATMOMETRY AND THE POROUS CUP ATMOMETER* 



BURTON EDWARD LIVINGSTON r ;«*"~ 



The Johns Hopkins University, Baltimore, Md. .-/,■ ■#' ^»9^ 



I 



INTRODUCTION 



The importance of the porous cup atmometer in studies of 

 plant and animal environment, and the fact that the literature 

 of the instrument fails to present, in adequate manner, several 

 very important considerations in regard to operation and in- 

 terpretation of atmometric readings, have led to the presentation 

 of this paper. For the sake of completeness it is here attempted 

 to state all essential points as far as they have been worked out, 

 whether or not such statement may involve repetition from the 

 writer's earlier papers. In short, this publication aims to put 

 before the worker in porous cup atmometry the various matters 

 requiring his attention, many of which might not be appre- 

 ciated without years of experimental acquaintance with the 

 subject. 



►Since so many names for the atmometer have been proposed 

 by various writers, it is perhaps not out of place here to state 

 that the term now practically in general use was first employed 

 by Leslie 2 in 1813. This word was adopted as official by the Com- 

 mittee on Evaporation of the Vienna Meteorological Congress 

 in 1874. The committee emphasize the fact that the word 

 atmometer "possesses the merits of seniority and a correct 

 classical derivation." It is constructed on parallel lines with 

 the familiar barometer, thermometer, hygrometer, anemometer, etc., 

 and thus enters readily into climatological and meteorological 

 discussion. 



1 Botanical contribution from the Johns Hopkins University, no. 43. 



2 Leslie, J., A short account of experiments and instruments depending on the 

 relations of air to heat and moisture. Edinburgh, 1813. 



21 



THE PLANT WORLD, VOL. 18, NO. 2, 1915 



