ON THE SUPPLY OF WATER TO TOWNS. 73 



the evidence of Dr. Hassall. The Severn at Gloucester contains palpable 

 indications of the sewage of Cheltenham, Tewkesbury and Worcester, and 

 the Ch'de at Glasgow is no longer fit for domestic use. Except, indeed, in 

 mountain districts of such physical and geological character that the water 

 can neither be injured by agricultural or mining operations, nor by the refuse 

 of towns and manufactures, few rivers can be depended upon for a supply of 

 good and wholesome water. 



I now pass on to the consideration of the supplies derived — 



4. From " gathering grounds" where the surplus-water of ivet seasons is 

 collected into large storeage reservoirs. — From these sources probably the most 

 important supplies are now derived, and many points of considerable interest 

 enter into the consideration of this branch of the subject. 



Very accurate information is required as to the fall of rain, the loss by 

 evaporation and vegetable absorption, the quantity of water which issues in 

 springs or flows off the surface of the ground, the duration of droughts and 

 the largest quantity of water which passes off the ground in limited periods, 

 together with the requisite capacity of reservoirs for storing such water 

 according to the character of the district or the annual amount of rain. 

 Nearly all the correct information which we possess on these points has 

 been collected within the last thirty years, the bulk of it within little more! 

 than half that period. So little was formerly known on these questions, 

 that so recently as 1799 the late Dr. Dalton wrote a paper which was read 

 before the Manchester Literary and Philosophical Society, entitled " Ex- 

 periments and Obi-ervations to determine whether the quantity of Rain and 

 Dew is equal to the quantity of Water carried off by Rivers and raised by 

 Evaporation, with an inquiry into the origin of Springs." In this paper he 

 examines the question by the aid of such meagre information as then existed, 

 and arrives at the conclusion, " that the rain and dew of this country are 

 equivalent to the quantity of water carried off by evaporation and by the 

 rivers." He then examines the various opinions which at that time existed 

 upon the origin of springs, combating the supposition that they were derived 

 from some hidden subterraneous source, concluding that they must be attri- 

 buted solely to the rain, their variation depending upon the seasons, and 

 upon the quantity of rain which falls. 



At this time Dr. Dalton determined that the average precipitation of rain 

 and dew throughout the kingdom was 36 inches, allowing 31 inches for rain 

 and 5 inches for dew. The highest returns of rain before him were from Ken- 

 dal and Keswick, both under 60 inches per annum. Observations since then, 

 some of the most important conducted by Dr. Miller of Whitehaven, have 

 proved that the rain in many parts of the country far exceeds this quantity. 

 In the mountainous district of Westmoreland and Cumberland, Dr. Miller has 

 ascertained that the rain amounts in one locality to nearly 200 inches 

 per annum. 



On the hills between Lancashire and Yorkshire it amounts occasionally to 

 80 inches in a year, the average being between 50 and 60 ; and from obser- 

 vations recently taken in the Highlands of Scotland, it exceeds, at the head 

 of Loch Katrine and Loch Lomond, 100 inches per annum. Judging by 

 analogy, and from such facts as have been ascertained, it is probable that 

 both amongst the mountains of Scotland and those of Wales, the rain will be as 

 great as Dr. Miller has ascertained it to be in the English lake district. Such 

 quantities form a striking contrast to those registered on the eastern coast of 

 the country, where the average will not probably exceed 20 inches per annum. 



The next important point is to ascertain how much of the rain which falls 



