180 EFFECTS OF FORESTS ON SPRINGS AND RIVERS. 



c. In the mean of the whole of the observations made in the several 

 years, 35J inches. 



" According to the views of Herr Maass the lowering of the heights 

 of the water level is not a consequence of any diminution of the 

 quantity of water now flowing into the Elbe, but the result of the 

 rectification of the river bed, an extensive deepening of this as a 

 consequence of that modification, and an increase of the rapidity of 

 the flow or delivery of the river. Herr Maass attaches importance to 

 the eiFects of these in lowering the level of the streams, and remarks 

 that no further lowering of that level is to be expected, because there 

 are no additional works of modification in contemplation. 



" As the observations and views of Herr Hagen and of Herr Maass 

 are diametrically opposed to observations which I have myself made 

 on several rivers during the last 40 years, I have brought together the 

 observations I have made on several rivers and streams, and the con- 

 clusions I have drawn from them, for publication as measurements of 

 the water level for many years, upon which reliance may be placed, 

 as it is only in being in possession of these data that I could have 

 been so bold as to come forward with any confidence as the opponent 

 of an authority so distinguished throughout the whole of Germany as 

 is Herr Hagen in matters pertaining to Hydrotechnics. 



"In the course of my observations on the subject in question there 

 came into my hands the remarkable work, Allgemeine Lander-und 

 Volkerkunde, by Dr Heinrich Bergman, — volume second, Umrises der 

 Hydrographie, for the year 1837,- — and I found in this work, and in 

 that issued by the same author and by J. Perthes, Hydro-hystorischen 

 Uebersiahten der deutschen Strome, for the year 1838, collected to- 

 gether much valuable material relative to the height of the water 

 and to the floating of the ice in the rivers. 



" From the observations on the river level made with the pegel at 

 Emmerich, on the frontier of Holland, for the period of 66 years, 

 from 1770 to 1835, and with these the observations made with the 

 pegel at Cologne for the period of 54 years, from 1782 to 1835, and 

 in addition to these the observations made on the Elbe with the 

 pegel at Magdeburg, for the period of 108 years, from 1728 to 1835, 

 and on the Oder with the pegel at Kiistrin, for the period of 58 years, 

 from 1778 to 1835, has the distinguished hydrographer Berghaus 

 determined the measurements of the highest and of the lowest levels 

 of these rivers, and from them calculated arithmetically the annual 

 mean levels. He has represented these by diagrams, and given 

 diagrams representative of the average height of the rivers in the 



