184 EFFECTS OF FOBESTS ON SPRINGS AND RIVERS. 



only about 10 lines, or five-sixths of an inch, for 50 years. And this 

 is explicable in that the bed of the stream has been at that place 

 reduced in breadth within later decades; and also in that the extensive 

 rectifications of the course of the Ehine, by cuttings above Manheim, 

 has made it possible that by means of sand and fine silt, transported 

 to the lower reaches of the river, the bed of the stream at Dusseldorf 

 may have become somewhat silted up and elevated in a way similar 

 to what has occurred to a still greater degree in the middle and lower 

 sections of the Elbe. 



" From the foregoing references it is evident that the conclusions 

 drawn by Herr Hagen, that the observations made up to this time on 

 the Khine do not indicate any general lowering of the water level, are 

 erroneous. And if he had been acquainted with the older observa- 

 tions at Emmerich and Cologne, published by Berghaus, or if he had 

 more skilfully compared the observations, extending over a period of 

 71 years, at Dusseldorf, he would probably have come to a conclu- 

 sion the very contrary to that to which he has come. 



"In order to obtain data on which reliance might be placed in regard 

 to the flow of the Ehine above Dusseldorf and Cologne, I addressed 

 myself to the distinguished hydrographer Herr Grebenau, Bavarian 

 Royal Bau-Inspector&i Gemersheim, who was for many years engaged 

 in the rectification of the new bed of the Rhine, and from him I re- 

 ceived not only the details of observations on the river-level at the 

 pegel at Sondersheim for the period of 28 years from 1840 to 1867, 

 but also the results of investigations on the delivery or quantity of 

 water passing each year through the cuttings of the Rhine bed at 

 Gemersheim, which Herr Grebenau had obtained with great care and 

 precision, partly by means of numerous special measurements of 

 vertical sections of the current and the rapidity of the flow, and 

 partly by means of calculations according to the latest formulas of 

 experimentally-obtained co-efficients. 



" When these tabulated observations on the water level, and the 

 diagram representative of the quantity of water delivered for the 

 period of 28 years, are divided into two successive periods of 14 years 

 each; and when for each of these there is calculated the means both of 

 the levels and of the delivery, there are obtained from these the 

 following results : the mean annual water level in the latter period of 

 14 years is about -432 mfetres, or 17'63 inches lower, and the delivery 

 is about 6966 cubic feet per second less, than in the former. 



" Along with this it must be admitted that, to a great extent, the 

 lowering of the mean annual level of the river is to be ascribed to a 



