On the Fall uf Rivers 311 



2d, The same results for the Lake of Tiberias are so much 

 at variance with the barometrical results, that it seems pro- 

 bable the latter (75G feet) would prove nearer to the true level. 

 3d, The fall of the Jordan of 984 feet between the two 

 lakes, as computed from the trigonometrical results, does not 

 exhibit an " immense contrast with all similar phenomena." 

 And, moreover, owing to our present defective knowledge of 

 the entire course of the Jordan, and the anomaly of the fall of 

 rivers in general, inferences drawn from the aggregate fall 

 of the Joi'dan can scarcely prove of sufficient weight to con- 

 trol the results of trigonometrical operations. 



I now beg leave to add a few data on the fall of some 

 rivers in this country, selecting such as might give a view of 

 the great variety of descents. 



The British Isles afford a wide field for the study of 

 hydrography ; and I have no hesitation in saying that it pos- 

 sesses for that study such extensive and valuable materials 

 and data as no other country can boast of; but, compara- 

 tively speaking, these materials have been drawn forward, 

 sifted, and made applicable for the pi'omotion of science to a 

 very limited extent. For example, the country has been 

 levelled in all directions, and especially along all rivers 

 of note, for the purpose of laying out canals and railways, 

 and yet we find little information in any work regarding ge- 

 neral results of the comparative fall of rivers. 



The levels in the following data are based upon authentic 

 documents, and relate entirely to the surface of the river 

 above the sea at low water. The distances have been for 

 the first time attempted to be ascertained with accuracy. 



I. The Shannon. — Tliis is the third largest river in the 

 United Kingdom, in regard to its basin.* As the fall of 

 rivers in general is greatest at their sources, and decreases 

 pi'oportionately towards their mouths, the Shannon in its de- 

 scent presents one of the rare exceptions to the general fall 

 of rivers, as it is greater in its lower than in its upper course. 

 Its source, the Shannon Pot, or more generally called Legna- 

 shinna, rises in the county of Cavan, between Upper Lough 



* The two larger rivers are thu Ihiiiilicr (including the Trent and the Ouse) 

 and the Severn. 



