SPHERICAL ATMOMETER CUPS 



A spherical evaporating surface, 5 cm. 

 in diameter, presenting the same external ex- 

 posure in all directions, with glazed cylindri- 

 cal neck 3 cm. long and 2 cm. inside diameter. 

 They are composed of very resistant material, 

 of proper porosity for atmometric work, and 

 are to be mounted on rubber stoppers as in 

 the case of cylindrical cups. The spheres may be cleaned with brush and distilled 

 water, may be treated with acid, and even heated to red heat. They should thus be 

 capable of many years of use, without permanent alteration of the coefficient. They 

 are not easily broken. 



These new spheres are supplied either standardized or unstandardized. Stand- 

 ardization is carried out with reference to a newly adopted spherical standard; spheres 

 cannot be satisfactorily standardized to the cylindrical standard cup. Therefore 

 readings from spheres are not satisfactorily reducible to terms of readings from cylin- 

 ders (see Plant World, Vol. 18, pp. 21, 51, 95, 143). 



Unstandardized White Splieres, $2.25 each, $20.00 per ten 

 Standardized White Spheres, $2.75 each, $25.00 per ten 



THE PLANT WORLD - - TUCSON, ARIZONA 



BLACK SPHERICAL 



ATMOMETER CUPS 



This is a porous porcelain sphere with matt black surface. The 

 dimensions and other specifications correspond to those of the white 

 spherical cup. The black spheres are sold only in the standardized 

 condition, being calibrated in terms of the spherical standard. They 

 may be operated with standardized white spheres for the measure- 

 ment of solar radiation, or may be used alone for the measurement 

 of evaporation in any work involving the rates from dark surfaces. 



For literature on the use of the Black Spherical Atm.ometer 

 Cup see The Plant World, Vol. 18, pp. 21, 51, 95, 143, or the pam- 

 phlet "Atmometry and the Porous Cup Atmometer." 



Standardized Black Spheres, $3.80 each, $36.00 per ten 



THE PLANT WORLD - - TUCSON, ARIZONA 



