140 



NEW YORK STATE MUSEUM 



As a consequence of (2) it is clear that a heavy rainfall on the 

 last days of any month may not appear at the point of gaging 

 until the next month. Mr Symons also states that the one great 

 fact which has been impressed upon him by these investigations 

 is the effect of winter frosts in regulating the flow of the river 

 Thames and in mitigating winter floods. 



These conclusions are more specially intended to apply to the 

 river Thames. Hence, while it is true that so-called negative 

 evaporation exists on all of the streams considered, the condi- 

 tions are nevertheless very different, and in the United States the 

 effect of holding back the flow of streams by frosts is in very many 

 cases to precipitate a flood of water later on. This element 

 would hardly be considered with us as either a river regulator or 

 as mitigating floods. 1 



Evaporation at Ogdcnshurg. Observations of the amount of 

 evaporation from water surfaces in New York were made by 

 Prof. James Coffin, Principal of Ogdensburg Academy, in 1838. 

 The following are Professor Coffin's results for the year 1838, as 

 taken from the Regents' reports for 1839 : 







Evapora- 



Mean 





Rainfall, 



tion, 



temperature 



Month 



inches 



inches 



F° 





2.36 



1.65 



24.8 



February 



0.97 



0.82 



12.3 



March 



1.18 



2.07 



32.9 



April 



0.40 



1.62 



39.8 



May 



4.81 



7.10 



52.5 



June 



3.57 



6.75 



66.5 



Julv 



1.88 



7.79 



71.7 



August 



vi.V 2.55 



- 5.42 



68.3 



September 



1.01 



7.40 



59.2 



October 



2.73 



3.95 



44.6 



November 



2.07 



3.66 



1>9.7 



December 



1.08 



1.15 



19.4 



Total 



24. 61 



49.36 



43.5 



Negative evaporation is discussed somewhat more extensively in the 

 writer's paper, The Relation of Rainfall to Runoff, than it is here. 



