128 Kansas Academy of Science. 



Two of the stations were located in Kansas, one at Lawrence, under 

 the auspices of the botany department of the University of Kansas, and 

 one at Tribune, under the auspices of the Kansas State Agricultural 

 College. The Lawrence station began its readings on August 7, 1916, 

 and the Tribune station on August 16, 1916, in the midst of the serious 

 drouth of that year. 



The data which have been accumulated during the last two years are 

 yet too meager to permit of any generalizations, but the mere facts have 

 proved to be so interesting that they deserve to be made public. 



The evaporation day by day has been plotted in the form of curves 

 for the thirteen months during which observations have been possible. 

 The winter months are omitted, of course, because the freezing of the 

 water would endanger the pan and still well, and would make accurate 

 readings impossible. The curves are shown on plates II to XIV. 



These curves are very irregular, due to rapidly changing conditions of 

 temperature, wind velocity, and relative humidity. The high points are 

 often associated with high temperature, or brisk winds, or both in ex- 

 treme cases. Unfortunately relative humidity data are not collected by 

 these stations. The low points correspond to periods of rainfall, or low 

 temperature, or light winds, or combinations of these conditions. 



While each of the curves presents certain points of interest, the most 

 striking one is plate X, for July, 1917, which illustrates the development 

 of serious drouth conditions. The spring rains ceased on June 5, several 

 weeks earlier than usual, and thereafter rainfall occurred as mere traces, 

 or in insignificant amounts until August 6. About the middle of July 

 (13-15), there were several small rains, following which the evaporation 

 increased steadily to the end of the month, reaching on July 30 the 

 highest daily rate ever recorded at the station, .709 inch. The maximum 

 temperature was above 100° every day for the last six days preceding 

 the 30th, and the wind velocity was high and constantly increasing dur- 

 ing the last four days of this period. This climax to the long dry period 

 came very near to being ruinous to crops, and would have been exceed- 

 ingly destructive if copious rains had not fallen at the end of the first 

 week in August. 



It is interesting to note that the average daily evaporation during the 

 drouth of August, 1916, was .330 inch per day, and the average daily 

 evaporation for the drouth of July, 1917, was .357 inch per day. Per- 

 haps it is not going too far to say that whenever the evaporation reaches 

 an average of about .350 inch per day for a week or two ot a time, drouth 

 conditions are rapidly approached in eastern Kansas. The evaporation 

 will not reach this level and maintain it until the weather has been dry 

 for some time, and the soil has become too dry to contribute much to the 

 humidity of the atmosphere. As long as the soil has a good supply of 

 moisture near the surface, the evaporation does not reach the drouth 

 level continuously, even though there is no rainfall. 



A comparison of the evaporation with rainfall month by month is 

 m.ost interesting. And the surprising thing about it is the almost con- 

 stant excess of evaporation over rainfall. The rainfall exceeded evapora- 

 tion in only two months out of the thirteen recorded, and one of these. 



