STATEMENTS BY HEBR HAGEN. 179 



thus found that in the course of the last 71 years, on the Ehone at 

 Dusseldorf, there has been a reduction of the highest floods to the 

 extent of 2"9 Hues, of the inean to the extent of 1'6 lines, while there 

 has been a rise in the lowest of 0-2 lines per annum. But on these 

 calculations Herr Hagen himself does not lay particular stress, as 

 there may be errors, he says, in the results obtained to the extent 

 of 2-2'", 0-9'", and 0-7'" respectively. 



" Herr Hagen says further : ' It may -well be imagined that in the 

 course of time a diminution in the highest and the meayi levels has 

 taken place ; and that for the reason that in later years, through the 

 modifications of the water-course which have occurred, the flotation 

 of ice has been impeded, the flow of water from the higher-lying 

 districts of the river's basin has been promoted ; whence the small 

 annual reduction of the calculated mean river-height may have 

 followed.' 



" Subsequently, Herr Hagen having expressed doubts in regard to 

 the statements of certain Hydrotechnikem, relative to a great 

 diminution in the level and delivery of the "Weser, from a comparison 

 of the observations made by the pegel at Minden and at Schliissel- 

 burg, comes to the following conclusion : ' It thence appears that, 

 in so far as observations made up to this time can show, it is as 

 impossible to give with certainty a verdict in regard to any general 

 diminution of its waters in regard to the Weser as in regard to the 

 Khone.' 



"Although the observations made on three gauges on two rivers 

 lead Herr Hagen to express himself thus guardedly on the subject of 

 a lowering of the water-level, yet the greater number of Hydrotechni- 

 kem — because observations continued through many yesirs, and com- 

 parison of the water-levels at distant periods of other rivers are not 

 at their command, and because they consider Herr Hagen an 

 infallible authority on all that relates to hydraulic engineering — ^have 

 come to the conclusion that in general there has not taken place any 

 great diminution in the flow and deliveiy of streams and rivers. 



" Herr Maass, the Prussian Royal Wasseriavr-Inspector, has 

 published, in the Zeitschrift fiir Bauwesen von Erhham, for the year 

 1870, observations of the height of the river Elbe for the period of 

 143 years, extending from 17-7 to 1S69, with a diagram represen- 

 tative of these observations ; and from these he has drawn the con- 

 clusions that within this period the waters of the Elbe have gradually 

 diminished in the foUowiug arithmetical means : a. In the highest 

 levels reached, 17 inches ; 6. In the lowest level observed, 34 inches; 



