Paper Atmometers for Studies in Evaporation. 287 



concave shell (3 or 4 mm. in depth) which fits perfectly upon 

 the rounded end of the paper cylinder. Across the center and 

 on the convex surface of this little glasr cap is cemented by its 

 middle (De Khotinsky cement is excellent) a short piece of 

 spiing brass wire (5 or 6 cm. long) slightly turned upward at its 

 ends. Two fine wires are affixed to the tin tube somewhat be- 

 low the free edge of the paper cylinder and these teiminate in 

 loops to pass over the hooked ends of the springs just mentioned, 

 when the glass cup is in place. The fine lateral wires must be of 

 such length that the proper amount of pressure will be exerted 

 upon the closed end of the paper cylinder. To place the clamp 

 in position, the glass cap is caiefully laid in position upon the 

 top of the thimble and pressure is applied with the fingers to 

 hold it and its cross-wire in place. The looped end of one lateral 

 wire is now hooked over one end of the cross-wire. Then the 

 opposite end of the latter is slightly flexed downward till the 

 second lateral wire is brought into place upon its hook. The 

 tension of the spring cross-wire thus distorted supplies the needed 

 pressure, and the tube may now be moved about with little 

 fear of air leakage. 



To prevent wind from loosening the paper cylinder, pressing 

 it against the tube on this side or the other, three or four tiny 

 bits of paratTined cork are cemented to the latter to form little 

 wedges upon which the free margin of the paper rests, or a deep- 

 ly fluted cork stopper is properly placed upon the tube. These 

 little coik piojecti'ns do not close the annular opening between 

 the tube and paper and ^et furnish to the latter the needed sup- 

 port. Thus arranged, the paper cylinder atmometer may be 

 safely exposed to the strong wind. Under very intense evapora- 

 tion the thimble must be shortened, otherwise its free edge be- 

 comes dry. 



Another method of affixing the paper cylinder to the tin 

 seat, which has given very good service in the open and which 

 possesses several advantages in the preparation, if not as many 

 in operation, is the following. Common red sealing wax is 

 melted in a suitable container and the closed end of 

 paper cylinder is diy^ped therein, so as to form a heavy, 

 very slightly elastic cap oi sealing wax a centimeter in height. 



