THE VEGETATION OF MONTAUK 67 



inclusive (1921) is instructive. As the graph shows, the rate per day of 

 the white instrument for that period was 26.5 cc. During the same time 

 the black instrument touched 49.3 cc, and in fact throughout the season, 

 the black, as would be expected, was consistently higher than the white. 

 But weather conditions during those four days ought not to have produced 

 such black readings, if current theories about that instrument are correct. 

 At Montauk this was the condition as to the main climatic features of these 

 four days, during which no rain fell. 







Total wind 















Max. 



Movement and 



Vap 



or Pressure 



Actual sun- 



Total Possible 



192 1 



Temp. 



Direction 





Inches 



shine hours 



sunshine hours 



July 25 



74 



442 mi. SW 





.646 





.■5- 1 



14.6 



26 



79 



389 mi. SW 





.732 





10.9 



14-5 



27 



77 



472 mi. SW 





.700 





6.0 



14-5 



28 



76 



627 mi. SW 





•715 





II.3 



14-5 



During two days of that period sunshine did not exceed 76% of the 

 possible, while during the other two it was not over 40% of the possible 

 and yet it is precisely sunshine that is supposed to affect the black instru- 

 ment most acutely. As the graph shows, this four day period had a higher 

 rate of evaporation than any other part of the season in spite of a partial 

 lack of sunshine during two of the days, and a serious lack of it on the other 

 two. But during those days the total daily movement of wind, and the 

 hourly velocity, were higher than for many days after. For the sake of the 

 record, I append the rate of the black atmometer on the Montauk Downs, 

 the maximum temperature, the vapor pressure, and wind velocity per 

 hour, for the "high spots" on the 1921 graph, together with actual and 

 possible amount of sunshine. 



Direction and 

 highest velocity Average 





Mean maximum 





of wind during 



vapor 



Actual 



Possible 



Reading 



temp, of 



each 



Evaporation 



period of at- 



pressure 



sunshine 



sunshine 



ending 



period 





per day in cc. 



mometer reading 



inches 



hours* 



hours 



July 28 



76 





49-3 



SW 40 mi. an 



.698 



8.3 



145 



Aug. 12 



75 





35-8 



SW 32 hour 



.617 



8.7 



13-9 



Aug. 18 



73 





40.0 



SW34 



•552 



7-5 



13-7 



Sept. 9 



76 





43-0 



SW22 



.556 



91 



12.8 



Sept. 24 



71 





450 



SW42 



•497 



II. 2 



12. 1 



* The actual hours have been calculated on the basis of taking the readings for each 

 day of the period ending on the dates in the left hand column, and averaging them. The 

 figure, then, means that during the period of atmometer readings ending with each date, 

 each day had on the average the number of hours sunshine given in the next to the last 

 column. 



