Passing out of the building and climbing a sloping bank, we now saw before us an expanse of water covering 3½ acres; but divided into two sections. Into the larger, the pump first delivers the water, that so much of the impurity as will form sediment may be precipitated. It then slowly glides through a small opening into the lesser section, which is a huge filter. ‘The impurities of water,’ said the barrister, assuming an oratorical attitude, to give us a taste of his ‘reading up,’ ‘are of two kinds; first, such as are mechanically suspended—say earth, chalk, sand, clay, dead vegetation or decomposed cats; and secondly, such as are dissolved or chemically combined—like salt, sugar, or alkali. Separation in the one case is easy, in the other it involves a chemical process. If you throw a pinch of sand into a tumbler of water, and stir it about, you produce a turbid mixture; but to render the fluid clear again you have only to adopt the simple process of letting it alone; for on setting the tumbler down for awhile, the particles—which, from their extreme minuteness, were easily disturbed and distributed amidst the fluid—being heavier than water, are precipitated, or in other words, fall to the bottom, leaving the liquid translucent. This is what is happening in the larger section of the reservoir to the chalky water of which we drank. I think I am correct?’ asked the speaker, angling for a single ‘cheer’ from the Engineer. ‘Quite so,’ replied that gentleman. ‘Provided the water could remain at rest long enough—which the insatiable maw of the modern Babylon does not allow,’—continued the honourable orator, rehearsing a bit more of his speech, ‘this mode of cleansing would be perfectly effectual. In proof of which I may only allude to Nature’s mode of depuration, as shown in lakes—that of Geneva for instance. The waters of the Rhone enter that expansive reservoir from the Valais in a very muddy condition; yet, after reposing in the lake, they issue at Geneva as clear as crystal. But so incessant is the London demand, that scarcely any time can be afforded for the impurities of the Thames, the Lea, or the New River to separate themselves from the water by mere deposition.’ ‘True,’ interjected one of the superintendants. ‘It is for that reason that our water is passed afterwards into the filtering bed, which is four feet thick.’ ‘How do you make up this enormous bed?’ ‘The water rests upon, and permeates through, 1st, a surface of fine sand; 2d, a stratum of shells; 3d, a layer of garden gravel; and 4th, a base of coarse gravel. It thence falls through a number of ducts into cisterns, whence it is pumped up so as to commence its travels to town through the conduit-pipe.’ We were returning to the engine-house, when Lyttleton asked the Engineer, ‘Does your experience generally, enable you to say that water as supplied by the nine companies, is tolerably pure?’ ‘Upon the whole, yes,’ was the answer.