July 30, 1917 Evaporation from Water and River-Bed Materials 



233 



PICHE EVAPORIMEJTER 



The Piche evaporimeter used is of the so-called improved type, 

 having a vent tube through the center opening at the top. It is grad- 

 uated in cubic centimeters, having a capacity of 40 c. c. The glass 

 plate is 9 cm. in diameter. It was hung in the instrument shelter. 



Table XI shows the evaporation figures resulting from its use. These 

 were not reduced to actual depths. A direct ratio between the evapora- 

 tion (in cubic centimeters) from the Piche instrument and tank 7 was 

 found in order to show the consistency of the results. Wind velocities 

 seem to have no direct bearing on this ratio. 



Previous experiments (i, p. 254) have been such as to warrant the 

 statement, "Estimated its accuracy as correct vnthin 20 per cent." 

 The data of the writers tend to show that the statement is not too con- 

 servative. Its use is not recommended when another type of evapo- 

 rimeter can be used, as it requires attention at more frequent intervals 

 than other types of evaporation-measuring devices. On particularly dry 

 days the tube would be empty within six hours after filling, and at such 

 times, while the tube contained water, this water could not flow to the 

 filter paper surface fast enough to prevent the drying and curling of the 

 edge. 



Table XI. — Relation between evaporation from water surface tank 7 {12 feet in diameter 

 by 3 feet in depth) and the Piche evaporimeter, Weather Bureau type 



Week ending — 



1916 



Apr. 24 a 



July 24 



31 



Aug. 7 



14 



21 



28 



Sept. 4 



II 



18 



25 



Oct. 2 



Total b 



Evapora- 

 tion from 

 tank 7. 



Inches. 

 I. 04 

 1.83 

 I. 76 

 1. 40 



1-43 

 I. 70 



1.47 

 1-57 

 1.82 

 .98 

 1.03 

 I- 15 



17. 18 



Evapora- 

 tion as 



shown by 

 Pische 



mevapori- 

 eter. 



C.c. 



187.0 



368.9 



319-4 

 181. 8 

 223. 8 

 280.8 

 217. 6 

 328.8 

 361.0 

 156.0 

 266. 2 

 225. 7 



3>"7-o 



Pische 

 evapora- 

 tion record 



-i- depth 

 from No. 7. 



180 

 201 

 180 



130 

 156 



148 

 209 

 198 



259 

 196 



c 181. 7 



Variation 



from mean 



ratio. 



P.d. 

 -0.9 

 -flO. 6 



- -9 



-28.5 

 -14. 2 

 -9.2 

 -18.6 

 + 15-0 

 + 9-5 

 -12. 5 

 -1-42.6 

 + 7-9 



Wind 

 movement. 



Miles. 

 860 



590 

 642 



532 

 634 



755 

 620 

 622 

 882 

 571 

 555 



"■ Records broken until July 17. 



3ii7-o_ 



- = 181.3. 



b Ratio of totals,- 



17.8 

 <^ Mean weekly ratio. 



