Lysimeter Experiments 17 



weather conditions, these data should accompany a statement of the 

 percolation. The physical properties of the soil under experiment have 

 already been described. The air temperatures at Ithaca, the hours of 

 sunshine, the average hourly velocity of the wind, and the humidity of 

 the air, are stated in table 4 of the appendix (pages 96-98) . No records 

 of evaporation for a free water surface have been kept at Ithaca, but 

 such data have been collected by the City Department of Engineering 

 at Rochester, New York, and these arranged by monthly averages are 

 given in table 5 of the appendix (page 98). In order to judge how closely 

 these data collected at Rochester are applicable to Ithaca, the rainfall, 

 the air temperature, and the air humidity at Rochester and at Ithaca^ 

 are given in table 6 of the appendix (page 99). 



It is seen from table 5 of the appendix that the evaporation from the 

 floating tub was 32.29 inches annually and that from the exposed tub 

 was 45.65 inches; while the rainfall for the same period was 27.89 inches 

 at the place where the evaporation records were taken, altho the Weather 

 Bureau readings at Rochester totaled 32.47 inches annually for the same 

 period. In either case the evaporation from the free water surface was 

 as great as or greater than the rainfall. The effect of the soil, therefore, 

 is to conserve moisture. A region that has no underground drainage 

 must have a very large rate of evaporation as compared with the rainfall. 



July is the month of greatest rate of evaporation and, except when the 

 ground is frozen, the month of least percolation, and August falls very 

 little behind in either respect. It is worthy of note, however, that there 

 is almost always some percolation from the unplanted soil thruout the 

 summer, altho the evaporation during that time is more than double 

 the rainfall (tables 2 and 5 of the appendix, pages 93-94 and 98). 



Experiments by other observers. — It may be of some interest to compare 

 the percentage percolation as found by the writers with that obtained 

 by some other observers. The percentage of the annual precipitation 

 that passes thru the soil, both when the soil is planted and when it is bare 

 of vegetation, has been determined at a number of localities. The most 

 complete data on this subject have been obtained at the Rothamsted 

 Experimental Station, Harpenden, England. The lysimeters at that 

 station were built around columns of soil and a perforated iron sheet 



1 The autliors are indebted to Mr. John F. Skinner for the compiled data on evaporation and weather 

 at Rochester, and to Professor W. M. Wilson for the weather records at Ithaca. 



2 17 



