264 



SCIENCE 



[N. S. Vol. XLV. No. 1159 



the construction of an accurate chart using 

 these data. It is pleasing, on this account, 

 that Dr. Livingston is distributing standard- 

 ized porous clap cup atmometers, and that 

 the Weather Bureau has adopted a standard 

 evaporation tank. For special purposes at a 

 given locality any type of atmometer which 

 fills the need is best. Thus, to determine the 

 evaporation from a reservoir surface, several 

 floating pans are used; for the study of evapo- 

 ration as affecting plant transpiration, some 

 form of water-impregnated paper or a porous 

 clay surface is to be chosen; and for soil 

 evaporation, a box or pan of moist soil is 

 logical. 



The porous clay cup atmometer, first sug- 

 gested by Babinet in 1848, modified by Living- 

 ston, Shive and "W. L. Tower and again by Liv- 

 ingston, is, in its present form, a spherical clay 

 cup 50 mm. in diameter or a clay plate 77 mm. 

 in diameter attached to a bottle of distilled 

 water.^^ Capillary attraction keeps the cup 

 full of water; and, when it rains, the water is 

 prevented from entering the instrument by 

 means of an ingenious mercury stopper in a 

 bend of the feeding tube. This instrument is 

 adapted especially to studies of plant and ani- 

 mal evaporation. The effect of the sun can be 

 measured by exposing a black and a white bulb 

 side by side. Frequent standardization is 

 necessary, although washing reduces the need. 

 It can not be operated in freezing weather; 

 but this is no drawback for most plant studies. 

 The atmometer is so compact and inconspicu- 

 ous that it can be exposed with safety almost 

 anywhere. 



The Weather Bureau standard is a galvan- 

 ized open pan four feet in diameter and ten 

 inches deep, which is kept clean and filled 

 with water to a depth of more than seven 

 inches. The top of the pan is some sixteen 

 inches above the ground. With the evap- 

 orating pan go anemometer, rain-gauge, and 

 maximum and minimum thermometers. When 



United States," Mo. Weather Bev., 16, 235-239, 

 1888. B. E. Livingston, "A Study of the Rela- 

 tion between Summer Evaporation Intensity and 

 Centers of Plant Distribution in the United 

 States," Plant World, 14, 205-222, 1911. 

 13 Science, N. S., XLI., pp. 872-874, 1915. 



set lip, the whole station is surrounded with a 

 substantial wire fence. By means of a still 

 well, and a micrometer, the depth of the water 

 is read every day at about 7 a.m. local time. 

 All water surface atmometers are subject to 

 the disadvantages (1) of wind action which 

 changes the form of the surface and may blow 

 some of the water out, (2) of the splash of 

 raindrops, and (3) of the interference of ani- 

 mals, birds and insects. Furthermore, the 

 water caught in the standard eight-inch rain- 

 gauge is not necessarily the same as that caught 

 in the tank. With all these errors, it seems 

 a mistake to carry the refinement of measure- 

 ment to the thousandth of an inch.^* 



While the results of the porous-cup observa- 

 tions and those from the evaporation pans 

 can not be used together, each in the course 

 of time will yield data sufiicient for the con- 

 struction of the first reasonably accurate 

 evaporation maps of the United States. 



EXTENSIONS OF THE WEATHER BUREAU SERVICE 



Out of the $81,210 increase in the appropria- 

 tions for the Weather Bureau for the current 

 fiscal year, $50,000 has been designated for ex- 

 tensions of the service. The largest item, 

 $30,000 is to be applied for the increase in 

 weather reports from the West Indies and 

 Central America. It is probable that some 10 

 new stations will be established, and that closer 

 cooperation between the Weather Bureau and 

 the meteorological services of Cuba and the 

 British colonies will be effected. If these plans 

 are carried out there will be about twice as 

 many stations in this region reporting twice 

 daily to the Central Ofiice during the hurricane 

 season, June 1 to November 30. The shipping 

 using the Panama Canal will be most bene- 

 fited. During, and for a few years after the 

 Spanish-American War, the Weather Bureau 

 maintained a service almost as extensive as 

 that now planned. 



$10,000 is to be used for more complete 

 organization of the weather observation work 



n Kadel, B. C, ' ' Instructions for the Installa- 

 tion and Operation of Class 'A' Evaporation Sta- 

 tions," Circular L, Instrument division, 1915, W. 

 B. No. 559, 8vo, 26 pp. 



