INFLUENCE OP WOODLANDS UPON STREAMS. 295 



extremes are especially noticed in the tables given for the Elbe and the 

 Vistula. As to the cause, this author remarks : 



The reason of this remarkable phenomenon is evidently this, that since many forests 

 have been cut oflF, more particularly on the mountains, heavy rains and deluging 

 showers occur more frequently ; and besides this, the soil being bare of trees the rain 

 penetrates less into the soil and more speedily reaches the streams and rivers, which 

 they fill to overflow ; and finally the mass of water tearing rapidly along, erodes the 

 mountain-sides that have been stripped of their forests, and fill up the channels of the 

 brooks and rivers with soil, sand, and rubbish, by which means their beds are raised, 

 and the water-surface is brought to a higher level. 



He then considers the evidences of failure of wells and springs, citing 

 various authorities, and ascribing these facts to the same cause. Ho 

 attributes to forests the faculty of condensing mists and clouds, and in 

 certain conditions the forming of rain, i)artly by their cooling efifect, and 

 the circulation of air which differences of temperature occasion, whereby 

 mists and clouds are formed and they are led to discharge rain. He 

 attributes this not so much to the forests themselves as to the differences 

 between the forests and the open fields by which these movements of 

 the air are produced that result in rain. The electrical influences of 

 forests, by their attraction, are also thought to increase the rainfall. A 

 part of the rains, by remaining upon the leaves, returns to vapor, and is 

 again precipitated as fog, mist, dew, or rain. 



The abundance of moisture in the woodlands, the facility with which 

 it percolates through the soil and reduces evaporation, all tend to the 

 maintenance of springs, and consequently of streams and rivers. The 

 drainage of lakelets, ponds, bogs, and marshes, and the cultivation of 

 the soil, all tend to reduce the volume of waters in streams, except as 

 discharged in heavy rains by surface-drainage, with great violence as 

 sweeping torrents and wide-spreading inundations. 



This paper has excited much interest, and its author having requested 

 the Imperial Academy of Sciences at Vienna to appoint a commission to 

 examine its facts and statements, it was done, and after several sessions 

 the commission reported their labors at a session held April 23, 1874.^ 

 After recapitulating the statements of the author, and the conclusions at 

 wbich he arrives, the commission proceed to notice some of the argu- 

 ments offered to the contrary from various sources, the principal of 

 which are as follows: 



1. The Prussian official, Oberbaurath, F. Eagen, from measurements of the Rhine, at 

 Diisseldorf, giving mean and maximum water-level, has noticed very small diminu- 

 tions (from 2.9 to 1.6 lines a year), which he ascribes to corrections lately made in the 

 stream, which j)revent the stoppage of ice, and facilitate the discharge of the high 

 water. 



'i. Herr Maas, Prussian inspector of works of hydrology, from tables running through 

 143 years, showing the stand of water in the Elbe, at the gauge near Magdeburg, found 

 a considerable decrease in extreme and mean dei^ths (from 17.35| to 34 inches), which 

 be attributes to changes brought on by constructions lately executed for regulating 

 the stream, which have lowered the bed, by increasing the velocity of the current. 



3. It has been presumed that discharge of water at mean and low stages is neutral- 

 ized by the high water, which occurs oftener of late years than formerly. 



The author sustains his views by the following facts : 



1. By measurements of the Ehine made at Sonderheim, through a period of 28 years, 

 by Herr Grebenau, showing not only the height of water, but by calculation the 

 amount passing that place, a corresponding decrease in amount is noticed. 



2. Observations by the commission for examining the Elbe show a deepening of the 

 stream-bed in its upper portions, and an elevation of the same from sand-deposits in 



'Vol. LXIX oi Proceedings of Royal Acad, of Sciences, April, 1874. This commission con- 

 sisted of Messrs. FenrJ, Jelinck, Von Schroter, Stefan, and Sues, to which Mr. Wex 

 was himself added. 



