BY THE HON. W. F. TAYLOR, M.D., ETC. 29 



mist. The evaporation from tropical seas is estimated at 100 

 inches per annum. About one-third of the rainfall runs off the 

 surface of gathering areas and is naturally impounded, forming 

 lakes, or is collected by rivulets and streams into rivers ; one- 

 third is evaporated, and the remaining third is absorbed by the 

 soil, and forms underground reservoirs. The amount in each 

 case varies according to the rapidity of rainfall and the character 

 of the surface of the ground. Dams constructed across the 

 outlets of gathering areas in hilly districts form storage reser- 

 voirs, which are largely availed of for the purpose of providing 

 a pure water supply to cities. One of the largest of modern 

 times has recently been completed at Thirlmere Lake, one of 

 the Cumberland lakes, at the foot of the Helvellyn mountain 

 range, for the purpose of increasing the storage capacity of the 

 lake, in order to afford an ample water supply to the city of 

 Manchester for many years to come. Thirlmere Lake was 

 originally 330 acres in area, and seventeen years ago a scheme 

 was projected to raise the lake an additional height of 50 feet 

 above its elevation from the sea level, in order to give the water 

 a sufficient fall on its way to Manchester, and to increase the 

 storage capacity of the lake by about 200 per cent. A huge dam 

 50 feet wide at its base and 18| feet wide at the top, carrying a 

 16 feet roadway, protected by parapets, has been constructed. 

 The area of the lake has been increased to 795 acres, and its 

 storage capacity is now 8,185,000,000 gallons. The gathering 

 area has a rainfall of 80 inches per annum — about 50,000,000 

 gallons per day for 150 days, even if no rain falls during that 

 time, will be available for Manchester. At present only 

 10,000,000 gallons per day will be required. The water is 

 carried over a space of nearly 100 miles from Cumberland to 

 Manchester — the longest distance traversed by water for the 

 supply of any city in the world. Of this distance 15 per cent, 

 had to be tunnelled — the remainder consisting of piping on a 

 large scale. In its long journey the water is twice carried over 

 rivers by means of siphon bridges, at the passage of the Eibble 

 and Lynn. 



Liverpool is supplied with water from Wales, a distance of 

 68 miles, the waters of the Vymwy having been impounded, and 

 an artificial reservoir 4f miles in length formed. 



