70 



BROOKLYN BOTANIC GARDEN MEMOIRS 



An examination of the graph of evaporation (Fig. 24) and of the details 

 of sunshine together with wind velocity, shows, during the period August 

 19-25, 1921, a good example of the fall of the evaporation rate of the black 

 instrument, in the face of better than the average rate of insolation. The 

 possible amount of sunshine during this period is 13.5 hours per day. The 

 actual sunshine for the period averaged 12.4 hours, which more nearly 

 approaches the possible amount than for any of the peak periods of the black 

 instrument. In the face of these seven days, when sunshine was nearly 

 at its maximum, there is, as the graph shows, a steadily falling rate of evapo- 

 ration from the black instrument. No rain fell during the period, and the 

 wind averaged but 22 miles per hour, while the mean maximum temperature 

 for the seven days was 70°. Comparison of these conditions with those of 

 the September 24 atmometer readings confirms the point. The maximum 

 temperatures then were one degree cooler, sunlight about one hour less, 

 and yet presumably, under the stimulus of a wind of 42 miles an hour 

 from the southwest, the black instrument climbed to 45.0 cc. of evaporation 

 per day. 



The maximum temperature, rainfall, vapor pressure, wind velocity and 

 prevailing wind direction together with the possible and actual amount of 

 sunshine, for the period of these 192 1 readings is here recorded, most of 

 the details of which have been kindly placed at my disposal by the Weather 

 Bureau station at Block Island. 



Evaporation Black and White Atmometers and Daily Maximum Temperatures> 

 Precipitation, Vapor Pressure, Direction and Velocity of Wind, Hours 

 Possible Sunshine and Hours Actual Sunshine. 

 Montauk Downs 192 i 



Date 



Max. 

 Temp- 

 era- 

 ture 



Rain- 

 fall 



Wind 

 veloc- 

 ity 



Wind 

 dir- 

 ection 



Hours 

 Possible 

 Sunshine 



Hours 

 Actual 

 Sunshine 



Vapor 



Pressure 



Inches 



Evaporation 



per day 



in cc. 





Black 



White 



July 





















15 



74 



•52 



38 



SW 



14.8 



0.9 



.67o\ 







16 



75 



.01 



22 



NE 



14.8 



6.7 



•569 1 







17 



75 





IQ 



S 



14.8 



12. 1 



•631/ 







18 



74 





26 



SW 



14.8 



9.2 



•646[ 







19 



75 



.24 



22 



s 



14-7 



1.2 



• 700\ 



29.8 



13-3 



20 



79 



1.28 



25 



w 



14-7 



10.7 



•639/ 







21 



68 





32 



N E 



14.7 



2.2 



.568I 







22 



71 





16 



E 



14-7 



8.9 



■5301 







23 



73 





16 



E 



14.6 



II. 7 



•575/ 







24 



76 





24 



S W 



14.6 



14.6 



.676/ 







