182 EFFECTS OF FORESTS ON SPRINGS AND RIVERS. 



parison, without reference to the fact whether in the course of these 

 33 years any rise or fall of the water-level had taken place, it is clear 

 that the above numbei's represent the reduction which had taken 

 place in the lowest levels and in the annual mean levels of the river 

 in the second period of 33 years — that is, for the half of the whole 

 period embraced by the observations made. 



"And the same remark will also apply to all subsequent com- 

 parisons of the water-level in two periods. 



" If we consider further the observations made of the pegel on the 

 Rhone at Cologne, from 1782 to 1835 [which was also appended to 

 the treatise], and again divide the period embraced of 54 years into 

 two consecutive periods of 27 years each, and by calculation deter- 

 mine the mean annual levels, we find that in the second of these 

 periods, that from 1809 to 1835, the mean height of highest floods 

 has risen about 0' V 66'" ; while, on the contrary, the mean annual 

 height has fallen about 4'27", and that of the lowest levels about 

 7 "21", as compared with those of the first half of the period, that 

 from 1782 to 1808. 



" From the foregoing deductions it is apparent that in the two 

 principal pegels on the Rhine at Emmerich and Cologne — during 

 the periods of 66 and of 54 years, embraced by them respectively 

 from 1770, and from 1782 to 1835 — there has taken place a not 

 inconsiderable fall both in the lowest levels and in the mean annual 

 levels ; and that only the mecm of the highest levels is found to be 

 somewhat higher in the second as compared with the earlier halves 

 of the periods embraced by the observations. 



"As during the period of observation extending from 1770 to 1835, 

 no such works of modification of the river's course as could have 

 produced any deepening of the bed of the stream at Cologne and at 

 Emmerich, or any increase of the rapidity of water-flow, and con- 

 sequent lowering of the water-level, had been carried on, the fall of 

 that level in the case of the lowest and the mecai states of the river, 

 during the later halves of the periods embraced by the observations 

 in question, can only be attributed to a diminished quantity of water 

 passing down the Rhine ; while the small rise in the annual mean of 

 the highest point reached, has to be ascribed to more frequent and 

 higher floods. 



" That the fall in the low and mean annual proves to be less than 

 it has been in some other rivers is accounted for, by Berghaus, by a 

 reference to the fact that the Rhine is fed, in a great measure, by the 

 confluence of numerous currents from the ice and snow on the Alps ; 



