juiyso, 1917 Evaporation from Water and River-Bed Materials 217 



blown away, or, without wind, it may cover the ice evenly. The larger 

 tank shown in Plate 34, C, has but little snow on the ice; the smaller has 

 considerable, frozen around the rim. Measurements from tanks of this 

 type where the water is frozen for a part of the year, while of some value, 

 do not necessarily show the true evaporation. 



Anemometer readings were taken to 0.1 mile, and in the test shown in 

 Plate 35, ^, the two anemometers at the ends checked within 0.2 mile 

 for 24 hours. A correction scale for the instrument in the center was 

 prepared from a two weeks' run, and an accuracy of about 0.4 mile in 24 

 hours was obtained in comparison with the two others. 



All thermometers used are calibrated to i degree ; readings were taken 

 to the nearest half-degree. Bach of the thermometers in use had been 

 compared with a standard thermometer, and in no case has a difference 

 in scale readings of more than 0.25° been found. Only the highest grade 

 instruments of recognized standard makes have been purchased. 



DETAJL WORK OP OBSERVATIONS 



The forms made up for work at the Denver laboratory show the read- 

 ings taken at each regular observation. In addition to these, there were 

 many additional records and check readings made. 



Two special forms are used. The first has the following columns: 

 "Date;" "Time;" general heading "Barometer," under which come 

 "Attached thermometer," "Observed barometer," "Correction," "Cor- 

 rected barometer;" general heading "Thermometer," under which are 

 "Set maximum," "Minimum," "Maximum," "Wet," "Dry," "Dew 

 point," "Relative humidity;" the general heading "Precipitation," 

 covering "Beginning," "Ending," "Rain gage No. i (inches)," "Rain 

 gage No. 2 (inches)," "Snowfall (inches);" and the heading "Wind," 

 which is subdivided into "Direction at time," "Anemometer No. i, 

 movement since last reading," "Anemometer No. 2, movement since last 

 reading," " Hours since last reading;" and several columns for remarks or 

 additional readings. The second form is used for evaporation alone and 

 has the columns headed: "Date;" "Time;" "Hours since last observa- 

 tion;" general heading "Evaporation Tank No.," which covers the 

 observations on that particular tank; "Hook gage, evaporated since last 

 observation," a blank column for filling notes, maximum thermometer, 

 minimum thermometer. Space for five evaporation tanks and remarks 

 is available on one form. 



New record sheets are required each week on the thermograph for air, 

 thermograph for v/ater, hydrograph and barograph. These changes are 

 made Monday forenoon. Twenty-four hours are covered by each sheet 

 of the anemometer register, and the requirement of new sheets for the 

 evaporimeter depends upon the rate of evaporation. 



