432 APPENDIX. 



NOTES TO CHAPTER III. 



P. 63. Investigations in Forest Meteorology. — The results 

 of the Bavarian observations, as well as the methods pursued, 

 were published by Dr. Ernst Eberraayer in " Die physikalischen 

 Einwirkungen des Waldes auf Luft und Boden und seine 

 klimatologische und hygienische Bedeutung," Berlin, 1873. 

 A very full summary is to be found in F. B. Hough's " Report 

 upon Forestry,'' Vol. I, Washington, Government Printing 

 Office, 1878. A more complete discussion of the whole 

 question and record of the investigations into "forest in- 

 fluences " is to be found in Bulletin 7, Division of Forestry, 

 U.S. Department of Agriculture, 1887, with further additions 

 to be found in H. R. doc. 181, 5Sth Congress, 3d session, 

 1899, from which sources the following data are reproduced. 



P. 64. Inefficiency of Rain Gauges.^ The inaccuracy of 

 the rainfall measurements by the ordinary unprotected gauges 

 is explained by Mr. Cleveland Abbe, in the Bulletin cited, as 

 follows : " In the case of ordinary rainfalls we invariably 

 have the air full of large and small drops, including the finer 

 particles that constitute a drizzling mist and the fragments of 

 drops that are broken up by spattering. All these are de- 

 scending at various velocities which, according to Stokes, 

 depend on their size and density and the viscous resistance of 

 the air ; the particles of hail descend even faster than drops 

 of water, and the flakes of snow descend slower than ordinary 

 drops. Now, when the wind strikes an obstacle, the deflected 

 currents on all sides of the obstacle move past the latter more 

 rapidly; therefore the open mouth of the rain gauge has 

 above it an invisible layer of air whose horizontal motion is 

 more rapid than that of the wind a little distance higher up. 

 Of the falling raindrops, the larger ones may descend with a 

 rapidity sufficient to penetrate this swiftly moving layer, but the 

 slower falling drops will be carried over the leeward of the 

 gauge, and, failing to enter it, will miss being counted as rain- 

 fall, although they go on to the ground near by. Evidently, 



