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NEW YORK STATE MUSEUM 



there is at the same time an atmosphere more or less saturated, 

 with an absence of sunshine; while in dry seasons the scarcity of 

 rain results in great dryness of the soil, with scant, slow evapora- 

 tion. 1 



Negative evaporation. In a strictly scientific sense this term is 

 taken to mean that when the temperature of the evaporating sur- 

 face is lower than the dewpoint, water is deposited on that sur- 

 face. As regards the rainfall, runoff, and evaporation tables, 

 herewith included, negative evaporation means that the runoff 

 for certain months is greater than the rainfall. Sometimes this 

 may legitimately happen when a heavy rainfall comes at the end 

 of the month, or when, with much snowfall, the temperature of 

 the month is mostly below freezing. In order to show as much 

 as possible in regard thereto, the writer gives the detail for each 

 of the tables of Muskingum, Genesee, Croton and Hudson rivers, 

 together with a tentative view as to the real significance of the 

 so-called negative evaporation. 



On Muskingum river, during the 8 years gaged, negative evapo- 

 ration is shown only twice for one month. 



On Genesee river the detailed tabulation shows negative evapo- 

 ration 5 times for one month and once for two consecutive months, 

 a total of 7 months in all. 



On Croton river, for the entire period of 32 years, negative 

 evaporation is shown 29 times for one month and 6 times for two 

 consecutive months, a total of 41 months in all. 



On Hudson river negative evaporation is shown 7 times for one 

 month and 4 times for two consecutive months, a total of 15 

 months. 



The writer has no doubt that, except in very cold climates, when 

 negative evaporation occurs for three or more consecutive months, 

 there is an error in the gagings. He also doubts their accuracy 

 somewhat when negative evaporation appears for two consecutive 

 months. As regards the storage period, there is no difficulty in 



1 Since the presistency of evaporation has been extensively discussed in 

 the writer's paper on Stream Flow in Relation to Forests, it is merely 

 touched on here. 



