244 



summer, and the loss ascertained must be taken to be the 

 maximum, and what the minimum may be is uncertain. The ; 

 average yearly loss I think is not less than half the rainfall, '• 

 after deducting for evaporation, leaving eight or nine inches of 

 water over the Under Oolite. The available depth over the 

 other strata in this Watershed may be taken at twelve inches. 

 Assuming it to be nine inches only, and the inhabitants of 

 London to be 3,250,000, then 272 square miles of Watershed at 

 this depth will supply them with thirty gallons each per day. ^ 

 It will thus appear that the Watersheds of the Churn, Ampney 

 and Marston brooks, the Coin, and of the Ock, amounting to 

 292^ square miles, will more than supply the entire population 

 of London. The Churn, the Coin, and the Windrush, having 

 an aggregate Watershed of 301 square miles, are more than 

 sufficient for the purpose; and the Watersheds of the Churn, 

 Coin, and the Ock, containing 260 square miles, are nearly 

 sufficient for the purpose. London is at present said to be 

 suppUed with 643,000 cubic yards (equal to 108,000,000 gals.) 

 of water daily, which is at the rate of more than thirty-three 

 gallons per head for three millions and a quarter of inhabitants. 

 If this be correct, London is more abundantly supplied than 

 many other towns. 



In the summer of 1 864, the Earl of St. Germans decided on 

 deepening and improving the Thames below and adjoining his 

 property, with the view of obtaining a better outfall for the 

 drainage which had been executed on the Down Ampney Estate. 

 This estate is bounded by the Thames, from the town of 

 Cricklade to near Castle Eaton, in distance more than three 

 miles. 



In August of this year, (1864) we found the water sufficiently 

 low to enable us to commence the works, and on the 24th of 

 that month we succeeded in confining nearly all the water 

 descending the river into a definite space of twelve feet in width. 

 I carefully ascertained the velocity and depth, and found that 

 thirteen millions of gallons were passing in twenty-four hours, 

 with every prospect of fine weather. This observation was 

 made towards the ripper part of Marston Meadow, about half a 

 mile to three-quarters of a mile above Castle Eaton Bridge. 



