STATEMENTS BY DR BERGHAUS. 181 



diflferent months of the year, and of the movement of the ice and of 

 floods ; and finally, he has in addition to these tabulated statements 

 given others illustrative of the influence of the rainfall on the 

 quantity of water carried off by the rivers, and has exhibited this in a 

 way so thorough and efficient as is not equalled in any other work on 

 Hydrotechnics. By which means Berghaus as a precursor has shown 

 to Hydrotechnikern in what way observations on the ever-varying 

 levels of rivers should be brought together and compared, in order to 

 present a distinct picture of the hydrographic phenomena, or of the 

 river life of the stream, and from this correctly to draw inferences 

 and final conclusions. 



" Fi-om these extremely detailed and deeply interesting investiga- 

 tions by Berghaus I make, amongst others, the following leading 

 deductions : — 



" From the ' Hydrographie ' of Dr Berghaus I have prepared a 

 diagram, which I have appended to this treatise, in which I have 

 represented what were the highest, and the lowest, and the calculated 

 mean annual water-levels of the Rhone, observed by the pegel at 

 Emmerich, from the year 1770 to 1835. From this diagram it 

 appears at a glance that the water-level of the several years is very 

 far indeed from being regular, but in successive years they rise and 

 fall ; and it is consequently difficult to represent by a continuous 

 line, or to calculate a mean representative of the diminution or 

 increase of the water-level for a period of some length, as HeiT Hagen 

 also states to *be the case. I therefore hold to the opinion that the 

 method adopted by Dr Berghaus, comparing the arithmetical mean of 

 the water-level during a more lengthened period than two years, is 

 more easy and supplies data upon which more reliance can be placed ; 

 and from the data thus procured, inferring or deducing whether there 

 has been any rise or fall in the river-level. If, then, we divide the 

 observations made during the period of 66 years into those made in 

 the first period of 33 years, from 1770 to 1802, and those made in 

 the second period of 33 years, from 1803 and 1835 ; and if from these 

 two equal periods of 33 years each we calculate and compare the annual 

 average levels of the river in each, the result will be, we shall find 

 that in the second period the average height of that level was 10'" in 

 excess of the first ; but on the contrary, the annual water-level has 

 fallen 1' 42" 5'", and the lowest 1' 1* 3"', when compared with the 

 corresponding earlier period from 1770 to 1802. 



"As the arithmetically determined mean of the river-level in the 

 first period, from 1770 to 1802, was only taken incidentally for com- 



