XVIII. 
WATER AND WATER-SUPPLY, 
WITH SPECIAL REFERENCE TO THE SUPPLY OF LONDON 
FROM THE CHALK OF HERTFORDSHIRE. 
By John Hopkinson, F.L.S., P.G.S., F.B.Met.Soc., President. 
Read at Hitchin, \2>th March % 1891.* 
PLATE IY. 
Water being the chief necessary of life, its presence on the surface 
of the earth, or within easy access underground, has been the most 
potent factor in determining the position of sites for human habita¬ 
tion in all parts of the world. Most of onr chief towns, and all our 
older cities, towns, and villages, are situated on the banks of rivers, 
the water in which, so long as it was uncontaminated, would form 
the only source of supply for drinking and other purposes. As the 
population increased and the towns extended, first along the river- 
banks and then at a distance from them, other sources of supply 
would be sought; and for ages the presence of a superficial stratum 
of sand or gravel over a bed of clay must have determined the direc¬ 
tion of growth, for in such strata water would easily be obtained by 
sinking shallow wells. 
Water is present almost everywhere, and often in a far larger 
proportion than might be supposed. It forms more than 70 per 
cent, of our own bodies, even our bones and muscles being largely 
composed of it, and the proportion in the vegetables we eat is from 
75 to 95 per cent., while some fruits contain a still larger proportion. 
It is universally present in the atmosphere in very varying propor¬ 
tions, but averaging about 1 \ per cent, when quite invisible. 
Without it everything on the earth would be scorched, while the 
direct rays of the sun, however intense, would scarcely warm the air 
in the slightest degree. But for the moisture ever present we could 
not bear the sun’s heat-rays, while the air, in the shade, were it 
not for radiation of heat from the earth, would be more intensely 
cold than we can possibly imagine, or than we could possibly bear. 
It is universally present in the earth as far down as we have been 
enabled to penetrate, entering into the composition of all kinds of 
rocks, even such as are as compact in structure as glass. It is not 
every rock, however, from which we can procure water. We could 
not possibly get a supply from our Hertfordshire Conglomerate, but 
we could drive off a considerable quantity of water of consolidation 
by calcining it. On the other hand, soft chalk, which, Prof. Ansted 
says, “ will take up half its own bulk of water and yet hardly 
appear wet,” f will part with it freely. Chalk, therefore, like sand¬ 
stone, is a valuable water-bearing rock, and although water percolates 
more rapidly through sandstone than it does through chalk, this is 
* Including portions of papers read at St. Albans, 18th Dec. 1890, and at 
Hertford, 27th Jan. 1891. 
f ‘Applications of Geology to the Arts and Manufactures,’ p. 56. 
VOL. VI.—PART V. 
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