Yol. 70.] AN]N T IYEBSABT ADDBESS OF THE PBESIDEXT. XCV 



the danger that muddiness in the water might be due in part to 

 human interference. Moreover, our experiments were not suf- 

 ficiently exhaustive to show whether the same proportion of 

 suspended matter was to be expected with the same velocity 

 of current, and whether the amount was the same with a rising as 

 with a falling river. The dissolved matter, on the other hand, 

 was expected to reach its maximum when the river was at its 

 lowest, and was being fed by springs ; it was expected to be at a 

 minimum when the river was in flood, and was being fed by rain- 

 water flowing directly off the surface of the ground. 



Some of our diagrams confirmed these anticipations. In the Exe 

 especially, a river which is more nearly than the others in a natural 

 condition, the curves representing suspended and dissolved matter 

 varied inversely with considerable regularity. In the Medway the 

 diagram, was impaired by our comparative failure to secure a 

 continuous record of the discharge of water. 



The Severn observations showed anomalies, which we could only 

 attribute to artificial interference in its course through a populous 

 region. A remarkable record, which could not be thus explained 

 away, was obtained by Dr. Woollatt during a period of frost and 

 thaw with snow. The proportion of suspended matter was ex- 

 tremely high at the commencement of the snowfall, which was 

 accompanied by heav}?" rain. Subsequently, while the snow was 

 disappearing, the proportion became abnormally low and so con- 

 tinued until normal conditions were restored. 



The experiments, which I have here mentioned briefly and 

 only so far as they have a geological bearing, will be described in 

 full in the publications of the Eoyal Geographical Society. They 

 were undertaken with the hope of ascertaining what ought to be 

 done, and what it is possible to do, in the investigation of the 

 phenomena which arise in a given area from the precipitation of 

 water in the form of rain and its discharge in the form of rivers. 

 In any future investigation, the five heads under which we carried 

 out our work must form the basis of operations. Two only are 

 provided for, namely, the ' Rainfall ' by the British Rainfall 

 Organization, and the ' Character of the Rocks ' by the Geo- 

 logical Survey ; for the other three additional organization would 

 be required. 



The importance which is attached to hydrographic surveys in 

 other countries is due to the fact that much of the ground covered 



