AND THE HERTFORDSeiUE BOURNE. 81 



that in these experiments at Rothamsted the surface of the ground 

 is kept in an artificial condition which is highly conducive to 

 excessive percolation, by which the excess of six inches would 

 probably be reduced to about four inches through soil in its natural 

 state, there is no need to fall back upon the supposition of a reserve 

 store of underground water to account for the flowing of the 

 Uourne in 1897, although this supposition is most probably correct. 



In the period referred to the Bourne has always flowed when the 

 percolation at Rothamsted has exceeded 26 per cent, of the average, 

 and never when the excess was less than 26 per cent. ; it flowed in 

 1876 when the excess icas 26 per cent. ; and it did not flow in 

 1892 with the same excess of percolation. 



An inch of rain falling on an area of a square mile yields nearly 

 14.^ million gallons of water. The catchment-basin of the Bourne 

 is at least five square miles in area. Each inch of rain which 

 percolates throughout this area down to the plane of saturation of 

 tlie Chalk should therefore yield at least 72^ million gallons of 

 water. When the Bourne was visited by the Society on the 24th 

 of April, 1897, the flow was about one million gallons a day. It 

 commenced to flow at the beginning of that month and ceased 

 before the end of June. It would not have flowed so fast at first, 

 and even by the, 19th of June the flow was very small indeed. It 

 is scarcely likely to have averaged a million gallons a day for 70 

 days, and therefore it is not likely that more than an inch in depth 

 of rain flowed over the surface of the ground. If we may form 

 any judgment of the probable percolation in the catchment-basin 

 of the liourne from the experiments at Rothamsted, the only 

 remarkable circumstance about the flowing of the Bourne in 1897 

 would be that it did not then flow from such a high point in the 

 valley, nor consequently in so great a volume, as it has done on 

 some previous occasions. 



CONCLITDING REMARKS. 



The facts here presented as to the flowing of the Hertfordshire 

 Bourne do not appear to me to confirm the deduction that there 

 has been a material depletion in our store of underground water in 

 the valley of the Colne and its tributaries, nor to negative such 

 an inference. It was about as likely that the Bourne would flow 

 in 1892 as it was that it would not, and it did not. I was certain 

 that it would flow in 1897, but it did not appear so early as 

 I expected it to do, for I went to look for it twice in March before 

 its outburst occurred. 



The valley of the Lea tells a very different tale. The decline 

 in the volume of the Chadwell Spring, and the total cessation 

 of the spring at Woolmers, in a period of more than average 

 rainfall, leave no room for doubt that there has been a very con- 

 siderable depletion in the store of water in that valley. There 

 must be something affecting the valley of the Lea which is not 

 affecting the valley of the Colne, or at least to any material extent. 

 In a quarter of a century the New River Company has increased the 



