July 30, 1917 Evaporation from Water and River-Bed Materials ^ ^ 5 



its use was discontinued, wind conditions being such that it was no 

 longer necessary. 



Instruments were installed for making quite complete meteorological 

 records to accompany the evaporation figures. All apparatus were of 

 the standard type in use by the Weather Bureau and w^ere accurately 

 calibrated. The location of the instrument shelter is shown in figure 2 

 and Plate 33. In addition to the maximum and minimum thermometer 

 equipment, it housed the Piche evaporimeter, thermograph, and hygro- 

 graph. Both sling and whirling psychrometers were used. Three ane- 

 mometers were in use, two being shown in figure 2 — No. i on a 14-foot 

 tower and No. 3 with cups about 2 feet above the ground to conform 

 with Weather Bureau specifications for class A evaporation stations. 

 The anemometer register attached to No. 3 is in the record office. No. 2 

 was located on the Washington Park Lake near by. The cups of this 

 instrument were about 2 feet above the water (PI. 37, 5). A test 

 run of the three instruments is shown in Plate 35, A. Four rain gages 

 were in use during the season — three at the laboratory, as shown on the 

 sketch, and one at the lake. 



Water temperature records were obtained by the use of maximum and 

 minimum thermometers with the bulb immersed to the depth 0.05 foot 

 in the tanks. The arrangement shown in tank 3 (PI, 34, B) was first 

 used. Later, the thermometers were floated in the water, held up by 

 means of a test tube i by 8 inches. This means allowed a control of the 

 depth of the bulb without adjustment after the installation and further 

 placed all metal under the surface. Careful comparisons showed that 

 the eflfect of this glass tube 3s not measurable, either in amount of evapora- 

 tion by a hook gage reading to o.ooi foot or in water temperature by 

 thermometers reading to i °, on a tank 2 feet in diameter. The thermom^ 

 eter tube without the metal mounting was tried, but the breakage in 

 wind made a continuance inadvisable. Floating maximum and mini- 

 mum thermometers in tank 8 are shown in Plate 37, A. P» thermograph 

 for water was attached to record continuously the temperature of the 

 water at the surface of No. 4. 



The barometer and barograph were located in the record office, 



OBSERVATIONS 



Tanks i to 8 were installed and were ready ior use on November i, 

 191 5. Observations were begun at that time, records of evaporation 

 being kept, and full readings from all meteorological instruments were 

 taken. Other tanks were added from time to time until the end of the 

 season 191 6. The dates of the increase of equipment are indicated by 

 the dates in the various tables presenting detailed results of the work. 



Throughout care has been taken to make all observations in accord- 

 ance with the rules of the United States Weather Bureau; and, in case 



